diff --git a/browser/actors/AboutNewTabChild.sys.mjs b/browser/actors/AboutNewTabChild.sys.mjs
index f22883166814..1eeed88e1ac8 100644
--- a/browser/actors/AboutNewTabChild.sys.mjs
+++ b/browser/actors/AboutNewTabChild.sys.mjs
@@ -10,8 +10,8 @@ import { PrivateBrowsingUtils } from "resource://gre/modules/PrivateBrowsingUtil
 
 const lazy = {};
 
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
+ChromeUtils.defineESModuleGetters(lazy, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
 });
 
 XPCOMUtils.defineLazyPreferenceGetter(
diff --git a/browser/actors/AboutPrivateBrowsingChild.sys.mjs b/browser/actors/AboutPrivateBrowsingChild.sys.mjs
index eda88e4b8993..1433c9cb799f 100644
--- a/browser/actors/AboutPrivateBrowsingChild.sys.mjs
+++ b/browser/actors/AboutPrivateBrowsingChild.sys.mjs
@@ -3,15 +3,13 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
-
 import { RemotePageChild } from "resource://gre/actors/RemotePageChild.sys.mjs";
 
 const lazy = {};
 
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-  ExperimentAPI: "resource://nimbus/ExperimentAPI.jsm",
+ChromeUtils.defineESModuleGetters(lazy, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
 });
 
 export class AboutPrivateBrowsingChild extends RemotePageChild {
diff --git a/browser/base/content/browser-sync.js b/browser/base/content/browser-sync.js
index f744bddbc99b..08b536533fe0 100644
--- a/browser/base/content/browser-sync.js
+++ b/browser/base/content/browser-sync.js
@@ -9,15 +9,11 @@ const { UIState } = ChromeUtils.importESModule(
   "resource://services-sync/UIState.sys.mjs"
 );
 
-ChromeUtils.defineModuleGetter(
-  this,
-  "ExperimentAPI",
-  "resource://nimbus/ExperimentAPI.jsm"
-);
-
 ChromeUtils.defineESModuleGetters(this, {
   EnsureFxAccountsWebChannel:
     "resource://gre/modules/FxAccountsWebChannel.sys.mjs",
+
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
   FxAccounts: "resource://gre/modules/FxAccounts.sys.mjs",
   SyncedTabs: "resource://services-sync/SyncedTabs.sys.mjs",
   Weave: "resource://services-sync/main.sys.mjs",
diff --git a/browser/base/content/browser.js b/browser/base/content/browser.js
index 8a6bc66381d8..67d6bcb3f45f 100644
--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -32,6 +32,7 @@ ChromeUtils.defineESModuleGetters(this, {
   Log: "resource://gre/modules/Log.sys.mjs",
   MigrationUtils: "resource:///modules/MigrationUtils.sys.mjs",
   NewTabUtils: "resource://gre/modules/NewTabUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   PictureInPicture: "resource://gre/modules/PictureInPicture.sys.mjs",
   PlacesTransactions: "resource://gre/modules/PlacesTransactions.sys.mjs",
   PlacesUIUtils: "resource:///modules/PlacesUIUtils.sys.mjs",
@@ -78,7 +79,6 @@ XPCOMUtils.defineLazyModuleGetters(this, {
   CFRPageActions: "resource://activity-stream/lib/CFRPageActions.jsm",
   CustomizableUI: "resource:///modules/CustomizableUI.jsm",
   DownloadUtils: "resource://gre/modules/DownloadUtils.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
   ExtensionsUI: "resource:///modules/ExtensionsUI.jsm",
   HomePage: "resource:///modules/HomePage.jsm",
   LoginHelper: "resource://gre/modules/LoginHelper.jsm",
diff --git a/browser/base/content/nonbrowser-mac.js b/browser/base/content/nonbrowser-mac.js
index d9dbed78fc3b..c1f6d2c2268c 100644
--- a/browser/base/content/nonbrowser-mac.js
+++ b/browser/base/content/nonbrowser-mac.js
@@ -5,8 +5,8 @@
 
 /* eslint-env mozilla/browser-window */
 
-XPCOMUtils.defineLazyModuleGetters(this, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
+ChromeUtils.defineESModuleGetters(this, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
 });
 
 let delayedStartupTimeoutId = null;
diff --git a/browser/base/content/test/about/browser_aboutSupport.js b/browser/base/content/test/about/browser_aboutSupport.js
index a9b1a1433125..d2fd38dfd30f 100644
--- a/browser/base/content/test/about/browser_aboutSupport.js
+++ b/browser/base/content/test/about/browser_aboutSupport.js
@@ -3,11 +3,11 @@
 
 "use strict";
 
-const { ExperimentAPI } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { ExperimentAPI } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 add_task(async function() {
diff --git a/browser/components/BrowserContentHandler.sys.mjs b/browser/components/BrowserContentHandler.sys.mjs
index 8a42bf114802..0b6aa0df4240 100644
--- a/browser/components/BrowserContentHandler.sys.mjs
+++ b/browser/components/BrowserContentHandler.sys.mjs
@@ -9,6 +9,7 @@ const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
   FirstStartup: "resource://gre/modules/FirstStartup.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
   SessionStartup: "resource:///modules/sessionstore/SessionStartup.sys.mjs",
   UpdatePing: "resource://gre/modules/UpdatePing.sys.mjs",
@@ -19,7 +20,6 @@ XPCOMUtils.defineLazyModuleGetters(lazy, {
   HeadlessShell: "resource:///modules/HeadlessShell.jsm",
   HomePage: "resource:///modules/HomePage.jsm",
   LaterRun: "resource:///modules/LaterRun.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
   ShellService: "resource:///modules/ShellService.jsm",
 });
 XPCOMUtils.defineLazyServiceGetters(lazy, {
diff --git a/browser/components/BrowserGlue.sys.mjs b/browser/components/BrowserGlue.sys.mjs
index cbc14f676b42..34e323fe8553 100644
--- a/browser/components/BrowserGlue.sys.mjs
+++ b/browser/components/BrowserGlue.sys.mjs
@@ -37,6 +37,7 @@ ChromeUtils.defineESModuleGetters(lazy, {
   Log: "resource://gre/modules/Log.sys.mjs",
   LoginBreaches: "resource:///modules/LoginBreaches.sys.mjs",
   NewTabUtils: "resource://gre/modules/NewTabUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   OsEnvironment: "resource://gre/modules/OsEnvironment.sys.mjs",
   PageDataService: "resource:///modules/pagedata/PageDataService.sys.mjs",
   PdfJs: "resource://pdf.js/PdfJs.sys.mjs",
@@ -91,7 +92,6 @@ XPCOMUtils.defineLazyModuleGetters(lazy, {
   ExtensionsUI: "resource:///modules/ExtensionsUI.jsm",
   HomePage: "resource:///modules/HomePage.jsm",
   NetUtil: "resource://gre/modules/NetUtil.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
   Normandy: "resource://normandy/Normandy.jsm",
 
   OnboardingMessageProvider:
diff --git a/browser/components/doh/DoHController.sys.mjs b/browser/components/doh/DoHController.sys.mjs
index 2d820aac21f4..0f53795cd1ad 100644
--- a/browser/components/doh/DoHController.sys.mjs
+++ b/browser/components/doh/DoHController.sys.mjs
@@ -15,17 +15,14 @@ ChromeUtils.defineESModuleGetters(lazy, {
   AsyncShutdown: "resource://gre/modules/AsyncShutdown.sys.mjs",
   ClientID: "resource://gre/modules/ClientID.sys.mjs",
   DoHConfigController: "resource:///modules/DoHConfig.sys.mjs",
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
   Heuristics: "resource:///modules/DoHHeuristics.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   Preferences: "resource://gre/modules/Preferences.sys.mjs",
   clearTimeout: "resource://gre/modules/Timer.sys.mjs",
   setTimeout: "resource://gre/modules/Timer.sys.mjs",
 });
 
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-  ExperimentAPI: "resource://nimbus/ExperimentAPI.jsm",
-});
-
 // When this is set we suppress automatic TRR selection beyond dry-run as well
 // as sending observer notifications during heuristics throttling.
 XPCOMUtils.defineLazyPreferenceGetter(
diff --git a/browser/components/extensions/test/xpcshell/test_ext_settings_overrides_search_mozParam.js b/browser/components/extensions/test/xpcshell/test_ext_settings_overrides_search_mozParam.js
index ce44c8080523..c05a24f2f8c5 100644
--- a/browser/components/extensions/test/xpcshell/test_ext_settings_overrides_search_mozParam.js
+++ b/browser/components/extensions/test/xpcshell/test_ext_settings_overrides_search_mozParam.js
@@ -9,8 +9,8 @@ const { AddonTestUtils } = ChromeUtils.import(
 const { SearchTestUtils } = ChromeUtils.importESModule(
   "resource://testing-common/SearchTestUtils.sys.mjs"
 );
-const { NimbusFeatures } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { NimbusFeatures } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
 const { sinon } = ChromeUtils.importESModule(
   "resource://testing-common/Sinon.sys.mjs"
diff --git a/browser/components/newtab/AboutNewTabService.jsm b/browser/components/newtab/AboutNewTabService.jsm
index dac03f14833b..6e04e32abf8c 100644
--- a/browser/components/newtab/AboutNewTabService.jsm
+++ b/browser/components/newtab/AboutNewTabService.jsm
@@ -42,8 +42,8 @@ const { E10SUtils } = ChromeUtils.importESModule(
 
 const lazy = {};
 
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
+ChromeUtils.defineESModuleGetters(lazy, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
 });
 
 /**
diff --git a/browser/components/newtab/aboutwelcome/AboutWelcomeChild.jsm b/browser/components/newtab/aboutwelcome/AboutWelcomeChild.jsm
index aeba680adfd9..07f4a692b84e 100644
--- a/browser/components/newtab/aboutwelcome/AboutWelcomeChild.jsm
+++ b/browser/components/newtab/aboutwelcome/AboutWelcomeChild.jsm
@@ -12,11 +12,14 @@ const { XPCOMUtils } = ChromeUtils.importESModule(
 
 const lazy = {};
 
+ChromeUtils.defineESModuleGetters(lazy, {
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
+});
+
 XPCOMUtils.defineLazyModuleGetters(lazy, {
-  ExperimentAPI: "resource://nimbus/ExperimentAPI.jsm",
   AboutWelcomeDefaults:
     "resource://activity-stream/aboutwelcome/lib/AboutWelcomeDefaults.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
 });
 
 XPCOMUtils.defineLazyGetter(lazy, "log", () => {
diff --git a/browser/components/newtab/lib/ASRouter.jsm b/browser/components/newtab/lib/ASRouter.jsm
index f04eda26cc67..0156c503d2ff 100644
--- a/browser/components/newtab/lib/ASRouter.jsm
+++ b/browser/components/newtab/lib/ASRouter.jsm
@@ -14,7 +14,9 @@ const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
   Downloader: "resource://services-settings/Attachments.sys.mjs",
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
   MacAttribution: "resource:///modules/MacAttribution.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   SpecialMessageActions:
     "resource://messaging-system/lib/SpecialMessageActions.sys.mjs",
   TargetingContext: "resource://messaging-system/targeting/Targeting.sys.mjs",
@@ -38,9 +40,7 @@ XPCOMUtils.defineLazyModuleGetters(lazy, {
     "resource://activity-stream/lib/ASRouterTriggerListeners.jsm",
   KintoHttpClient: "resource://services-common/kinto-http-client.js",
   RemoteL10n: "resource://activity-stream/lib/RemoteL10n.jsm",
-  ExperimentAPI: "resource://nimbus/ExperimentAPI.jsm",
   setTimeout: "resource://gre/modules/Timer.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
   Utils: "resource://services-settings/Utils.jsm",
 });
 XPCOMUtils.defineLazyServiceGetters(lazy, {
diff --git a/browser/components/newtab/lib/ASRouterTargeting.jsm b/browser/components/newtab/lib/ASRouterTargeting.jsm
index 38a637744300..8e978a96806d 100644
--- a/browser/components/newtab/lib/ASRouterTargeting.jsm
+++ b/browser/components/newtab/lib/ASRouterTargeting.jsm
@@ -24,6 +24,7 @@ const lazy = {};
 ChromeUtils.defineESModuleGetters(lazy, {
   AttributionCode: "resource:///modules/AttributionCode.sys.mjs",
   BuiltInThemes: "resource:///modules/BuiltInThemes.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   ProfileAge: "resource://gre/modules/ProfileAge.sys.mjs",
   Region: "resource://gre/modules/Region.sys.mjs",
   TargetingContext: "resource://messaging-system/targeting/Targeting.sys.mjs",
@@ -38,7 +39,6 @@ XPCOMUtils.defineLazyModuleGetters(lazy, {
   HomePage: "resource:///modules/HomePage.jsm",
   AboutNewTab: "resource:///modules/AboutNewTab.jsm",
   BrowserWindowTracker: "resource:///modules/BrowserWindowTracker.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
 });
 
 ChromeUtils.defineModuleGetter(
diff --git a/browser/components/newtab/lib/AboutPreferences.jsm b/browser/components/newtab/lib/AboutPreferences.jsm
index 4906728eb29c..476b42b21e93 100644
--- a/browser/components/newtab/lib/AboutPreferences.jsm
+++ b/browser/components/newtab/lib/AboutPreferences.jsm
@@ -3,9 +3,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 "use strict";
 
-const { XPCOMUtils } = ChromeUtils.importESModule(
-  "resource://gre/modules/XPCOMUtils.sys.mjs"
-);
 const { actionTypes: at, actionCreators: ac } = ChromeUtils.importESModule(
   "resource://activity-stream/common/Actions.sys.mjs"
 );
@@ -15,8 +12,8 @@ const PREFERENCES_LOADED_EVENT = "home-pane-loaded";
 
 const lazy = {};
 
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
+ChromeUtils.defineESModuleGetters(lazy, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
 });
 
 // These "section" objects are formatted in a way to be similar to the ones from
diff --git a/browser/components/newtab/lib/DiscoveryStreamFeed.jsm b/browser/components/newtab/lib/DiscoveryStreamFeed.jsm
index 2aa56f598ab6..af3b6c1152c7 100644
--- a/browser/components/newtab/lib/DiscoveryStreamFeed.jsm
+++ b/browser/components/newtab/lib/DiscoveryStreamFeed.jsm
@@ -5,6 +5,7 @@
 
 const lazy = {};
 ChromeUtils.defineESModuleGetters(lazy, {
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
   NewTabUtils: "resource://gre/modules/NewTabUtils.sys.mjs",
   Region: "resource://gre/modules/Region.sys.mjs",
   RemoteSettings: "resource://services-settings/remote-settings.sys.mjs",
@@ -25,11 +26,6 @@ ChromeUtils.defineModuleGetter(
   "PersistentCache",
   "resource://activity-stream/lib/PersistentCache.jsm"
 );
-ChromeUtils.defineModuleGetter(
-  lazy,
-  "ExperimentAPI",
-  "resource://nimbus/ExperimentAPI.jsm"
-);
 
 const CACHE_KEY = "discovery_stream";
 const LAYOUT_UPDATE_TIME = 30 * 60 * 1000; // 30 minutes
diff --git a/browser/components/newtab/lib/OnboardingMessageProvider.jsm b/browser/components/newtab/lib/OnboardingMessageProvider.jsm
index a805bfb0bc4c..590449770731 100644
--- a/browser/components/newtab/lib/OnboardingMessageProvider.jsm
+++ b/browser/components/newtab/lib/OnboardingMessageProvider.jsm
@@ -18,10 +18,10 @@ const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
   BrowserUtils: "resource://gre/modules/BrowserUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
 });
 
 XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
   ShellService: "resource:///modules/ShellService.jsm",
 });
 
diff --git a/browser/components/newtab/lib/PlacesFeed.jsm b/browser/components/newtab/lib/PlacesFeed.jsm
index 8e68ac5c6ed0..27ee47e038bd 100644
--- a/browser/components/newtab/lib/PlacesFeed.jsm
+++ b/browser/components/newtab/lib/PlacesFeed.jsm
@@ -3,10 +3,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 "use strict";
 
-const { XPCOMUtils } = ChromeUtils.importESModule(
-  "resource://gre/modules/XPCOMUtils.sys.mjs"
-);
-
 const {
   actionCreators: ac,
   actionTypes: at,
@@ -24,7 +20,9 @@ const { AboutNewTab } = ChromeUtils.import(
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
   NewTabUtils: "resource://gre/modules/NewTabUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   PartnerLinkAttribution: "resource:///modules/PartnerLinkAttribution.sys.mjs",
   PlacesUtils: "resource://gre/modules/PlacesUtils.sys.mjs",
   PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
@@ -34,14 +32,6 @@ ChromeUtils.defineModuleGetter(
   "pktApi",
   "chrome://pocket/content/pktApi.jsm"
 );
-ChromeUtils.defineModuleGetter(
-  lazy,
-  "ExperimentAPI",
-  "resource://nimbus/ExperimentAPI.jsm"
-);
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-});
 
 const LINK_BLOCKED_EVENT = "newtab-linkBlocked";
 const PLACES_LINKS_CHANGED_DELAY_TIME = 1000; // time in ms to delay timer for places links changed events
diff --git a/browser/components/newtab/lib/PrefsFeed.jsm b/browser/components/newtab/lib/PrefsFeed.jsm
index fb50fe48c64e..a511aa24f825 100644
--- a/browser/components/newtab/lib/PrefsFeed.jsm
+++ b/browser/components/newtab/lib/PrefsFeed.jsm
@@ -6,9 +6,6 @@
 const { actionCreators: ac, actionTypes: at } = ChromeUtils.importESModule(
   "resource://activity-stream/common/Actions.sys.mjs"
 );
-const { XPCOMUtils } = ChromeUtils.importESModule(
-  "resource://gre/modules/XPCOMUtils.sys.mjs"
-);
 const { Prefs } = ChromeUtils.import(
   "resource://activity-stream/lib/ActivityStreamPrefs.jsm"
 );
@@ -19,14 +16,11 @@ const { AppConstants } = ChromeUtils.importESModule(
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
   Region: "resource://gre/modules/Region.sys.mjs",
 });
 
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-});
-
 class PrefsFeed {
   constructor(prefMap) {
     this._prefMap = prefMap;
diff --git a/browser/components/newtab/lib/SectionsManager.jsm b/browser/components/newtab/lib/SectionsManager.jsm
index 81c052397e6e..3e9853203873 100644
--- a/browser/components/newtab/lib/SectionsManager.jsm
+++ b/browser/components/newtab/lib/SectionsManager.jsm
@@ -6,9 +6,6 @@
 const { EventEmitter } = ChromeUtils.importESModule(
   "resource://gre/modules/EventEmitter.sys.mjs"
 );
-const { XPCOMUtils } = ChromeUtils.importESModule(
-  "resource://gre/modules/XPCOMUtils.sys.mjs"
-);
 const { actionCreators: ac, actionTypes: at } = ChromeUtils.importESModule(
   "resource://activity-stream/common/Actions.sys.mjs"
 );
@@ -19,13 +16,10 @@ const { getDefaultOptions } = ChromeUtils.import(
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   PlacesUtils: "resource://gre/modules/PlacesUtils.sys.mjs",
 });
 
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-});
-
 /*
  * Generators for built in sections, keyed by the pref name for their feed.
  * Built in sections may depend on options stored as serialised JSON in the pref
diff --git a/browser/components/newtab/lib/TelemetryFeed.jsm b/browser/components/newtab/lib/TelemetryFeed.jsm
index 9f33b1d40f39..4aa00a4ace36 100644
--- a/browser/components/newtab/lib/TelemetryFeed.jsm
+++ b/browser/components/newtab/lib/TelemetryFeed.jsm
@@ -45,6 +45,8 @@ ChromeUtils.defineModuleGetter(
 );
 ChromeUtils.defineESModuleGetters(lazy, {
   ClientID: "resource://gre/modules/ClientID.sys.mjs",
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
   TelemetryEnvironment: "resource://gre/modules/TelemetryEnvironment.sys.mjs",
   TelemetrySession: "resource://gre/modules/TelemetrySession.sys.mjs",
@@ -61,11 +63,6 @@ ChromeUtils.defineModuleGetter(
   "resource://gre/modules/ExtensionSettingsStore.jsm"
 );
 
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  ExperimentAPI: "resource://nimbus/ExperimentAPI.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-});
-
 const ACTIVITY_STREAM_ID = "activity-stream";
 const DOMWINDOW_OPENED_TOPIC = "domwindowopened";
 const DOMWINDOW_UNLOAD_TOPIC = "unload";
diff --git a/browser/components/newtab/lib/ToastNotification.jsm b/browser/components/newtab/lib/ToastNotification.jsm
index 4d6193d76fcf..1664a8d60a2c 100644
--- a/browser/components/newtab/lib/ToastNotification.jsm
+++ b/browser/components/newtab/lib/ToastNotification.jsm
@@ -9,8 +9,11 @@ const { XPCOMUtils } = ChromeUtils.importESModule(
 
 const lazy = {};
 
+ChromeUtils.defineESModuleGetters(lazy, {
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
+});
+
 XPCOMUtils.defineLazyModuleGetters(lazy, {
-  ExperimentAPI: "resource://nimbus/ExperimentAPI.jsm",
   RemoteL10n: "resource://activity-stream/lib/RemoteL10n.jsm",
 });
 
diff --git a/browser/components/newtab/lib/TopSitesFeed.jsm b/browser/components/newtab/lib/TopSitesFeed.jsm
index 16ce5af2e2d0..ef1634843dc6 100644
--- a/browser/components/newtab/lib/TopSitesFeed.jsm
+++ b/browser/components/newtab/lib/TopSitesFeed.jsm
@@ -52,6 +52,7 @@ ChromeUtils.defineModuleGetter(
 );
 ChromeUtils.defineESModuleGetters(lazy, {
   NewTabUtils: "resource://gre/modules/NewTabUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   Region: "resource://gre/modules/Region.sys.mjs",
   RemoteSettings: "resource://services-settings/remote-settings.sys.mjs",
 });
@@ -73,10 +74,6 @@ XPCOMUtils.defineLazyGetter(lazy, "log", () => {
   return new Logger("TopSitesFeed");
 });
 
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-});
-
 const DEFAULT_SITES_PREF = "default.sites";
 const SHOWN_ON_NEWTAB_PREF = "feeds.topsites";
 const DEFAULT_TOP_SITES = [];
diff --git a/browser/components/newtab/test/browser/abouthomecache/browser_experiments_api_control.js b/browser/components/newtab/test/browser/abouthomecache/browser_experiments_api_control.js
index bcf1f066d681..a94f1fe05543 100644
--- a/browser/components/newtab/test/browser/abouthomecache/browser_experiments_api_control.js
+++ b/browser/components/newtab/test/browser/abouthomecache/browser_experiments_api_control.js
@@ -3,8 +3,8 @@
 
 "use strict";
 
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 registerCleanupFunction(async () => {
diff --git a/browser/components/newtab/test/browser/browser_aboutwelcome_configurable_ui.js b/browser/components/newtab/test/browser/browser_aboutwelcome_configurable_ui.js
index c7bebd5baedc..ff3ad2fce0e9 100644
--- a/browser/components/newtab/test/browser/browser_aboutwelcome_configurable_ui.js
+++ b/browser/components/newtab/test/browser/browser_aboutwelcome_configurable_ui.js
@@ -1,7 +1,7 @@
 "use strict";
 
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 const { AboutWelcomeTelemetry } = ChromeUtils.import(
diff --git a/browser/components/newtab/test/browser/browser_aboutwelcome_multistage_experimentAPI.js b/browser/components/newtab/test/browser/browser_aboutwelcome_multistage_experimentAPI.js
index b37b848745a1..fea1ca961ac5 100644
--- a/browser/components/newtab/test/browser/browser_aboutwelcome_multistage_experimentAPI.js
+++ b/browser/components/newtab/test/browser/browser_aboutwelcome_multistage_experimentAPI.js
@@ -1,10 +1,10 @@
 "use strict";
 
-const { ExperimentAPI } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { ExperimentAPI } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 const { TelemetryTestUtils } = ChromeUtils.importESModule(
   "resource://testing-common/TelemetryTestUtils.sys.mjs"
diff --git a/browser/components/newtab/test/browser/browser_aboutwelcome_rtamo.js b/browser/components/newtab/test/browser/browser_aboutwelcome_rtamo.js
index 7c53ea21b221..0bad44cba77c 100644
--- a/browser/components/newtab/test/browser/browser_aboutwelcome_rtamo.js
+++ b/browser/components/newtab/test/browser/browser_aboutwelcome_rtamo.js
@@ -6,8 +6,8 @@ const { ASRouter } = ChromeUtils.import(
 const { AddonRepository } = ChromeUtils.import(
   "resource://gre/modules/addons/AddonRepository.jsm"
 );
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 const TEST_ADDON_INFO = [
diff --git a/browser/components/newtab/test/browser/browser_asrouter_experimentsAPILoader.js b/browser/components/newtab/test/browser/browser_asrouter_experimentsAPILoader.js
index ad8af06ed449..ac2b8703a834 100644
--- a/browser/components/newtab/test/browser/browser_asrouter_experimentsAPILoader.js
+++ b/browser/components/newtab/test/browser/browser_asrouter_experimentsAPILoader.js
@@ -4,17 +4,17 @@ const { RemoteSettings } = ChromeUtils.importESModule(
 const { ASRouter } = ChromeUtils.import(
   "resource://activity-stream/lib/ASRouter.jsm"
 );
-const { RemoteSettingsExperimentLoader } = ChromeUtils.import(
-  "resource://nimbus/lib/RemoteSettingsExperimentLoader.jsm"
+const { RemoteSettingsExperimentLoader } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/RemoteSettingsExperimentLoader.sys.mjs"
 );
-const { ExperimentAPI } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { ExperimentAPI } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
-const { ExperimentFakes, ExperimentTestUtils } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes, ExperimentTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
-const { ExperimentManager } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentManager.jsm"
+const { ExperimentManager } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/ExperimentManager.sys.mjs"
 );
 const { TelemetryFeed } = ChromeUtils.import(
   "resource://activity-stream/lib/TelemetryFeed.jsm"
diff --git a/browser/components/newtab/test/browser/browser_asrouter_targeting.js b/browser/components/newtab/test/browser/browser_asrouter_targeting.js
index 025a6238d554..a79e6e0cefb9 100644
--- a/browser/components/newtab/test/browser/browser_asrouter_targeting.js
+++ b/browser/components/newtab/test/browser/browser_asrouter_targeting.js
@@ -5,10 +5,7 @@ XPCOMUtils.defineLazyModuleGetters(this, {
   ASRouterTargeting: "resource://activity-stream/lib/ASRouterTargeting.jsm",
   BrowserWindowTracker: "resource:///modules/BrowserWindowTracker.jsm",
   CFRMessageProvider: "resource://activity-stream/lib/CFRMessageProvider.jsm",
-  ExperimentAPI: "resource://nimbus/ExperimentAPI.jsm",
-  ExperimentFakes: "resource://testing-common/NimbusTestUtils.jsm",
   HomePage: "resource:///modules/HomePage.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
   QueryCache: "resource://activity-stream/lib/ASRouterTargeting.jsm",
   ShellService: "resource:///modules/ShellService.jsm",
 });
@@ -16,8 +13,11 @@ ChromeUtils.defineESModuleGetters(this, {
   AppConstants: "resource://gre/modules/AppConstants.sys.mjs",
   AttributionCode: "resource:///modules/AttributionCode.sys.mjs",
   BuiltInThemes: "resource:///modules/BuiltInThemes.sys.mjs",
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
+  ExperimentFakes: "resource://testing-common/NimbusTestUtils.sys.mjs",
   FxAccounts: "resource://gre/modules/FxAccounts.sys.mjs",
   NewTabUtils: "resource://gre/modules/NewTabUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   PlacesTestUtils: "resource://testing-common/PlacesTestUtils.sys.mjs",
   ProfileAge: "resource://gre/modules/ProfileAge.sys.mjs",
   Region: "resource://gre/modules/Region.sys.mjs",
diff --git a/browser/components/newtab/test/browser/browser_newtab_ping.js b/browser/components/newtab/test/browser/browser_newtab_ping.js
index d12f03d50ad2..35b3c2c35704 100644
--- a/browser/components/newtab/test/browser/browser_newtab_ping.js
+++ b/browser/components/newtab/test/browser/browser_newtab_ping.js
@@ -10,8 +10,8 @@ const { ASRouter } = ChromeUtils.import(
   "resource://activity-stream/lib/ASRouter.jsm"
 );
 
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 let sendTriggerMessageSpy;
diff --git a/browser/components/newtab/test/browser/browser_trigger_messagesLoaded.js b/browser/components/newtab/test/browser/browser_trigger_messagesLoaded.js
index fad36809225d..816871528926 100644
--- a/browser/components/newtab/test/browser/browser_trigger_messagesLoaded.js
+++ b/browser/components/newtab/test/browser/browser_trigger_messagesLoaded.js
@@ -8,14 +8,14 @@ const { ASRouter } = ChromeUtils.import(
 const { RemoteSettings } = ChromeUtils.importESModule(
   "resource://services-settings/remote-settings.sys.mjs"
 );
-const { RemoteSettingsExperimentLoader } = ChromeUtils.import(
-  "resource://nimbus/lib/RemoteSettingsExperimentLoader.jsm"
+const { RemoteSettingsExperimentLoader } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/RemoteSettingsExperimentLoader.sys.mjs"
 );
-const { ExperimentAPI } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { ExperimentAPI } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
-const { ExperimentFakes, ExperimentTestUtils } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes, ExperimentTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 const client = RemoteSettings("nimbus-desktop-experiments");
diff --git a/browser/components/pocket/content/pktApi.jsm b/browser/components/pocket/content/pktApi.jsm
index 50da6e6ab99b..c8fd09a79c48 100644
--- a/browser/components/pocket/content/pktApi.jsm
+++ b/browser/components/pocket/content/pktApi.jsm
@@ -50,13 +50,10 @@ const { XPCOMUtils } = ChromeUtils.importESModule(
 const lazy = {};
 ChromeUtils.defineESModuleGetters(lazy, {
   IndexedDB: "resource://gre/modules/IndexedDB.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
 });
 
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-});
-
 XPCOMUtils.defineLazyPreferenceGetter(
   lazy,
   "gCookieFirstPartyIsolate",
diff --git a/browser/components/pocket/content/pktUI.js b/browser/components/pocket/content/pktUI.js
index 9ce29b5874e9..37de5c139fc0 100644
--- a/browser/components/pocket/content/pktUI.js
+++ b/browser/components/pocket/content/pktUI.js
@@ -45,6 +45,8 @@
 /* eslint-env mozilla/browser-window */
 
 ChromeUtils.defineESModuleGetters(this, {
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
   ReaderMode: "resource://gre/modules/ReaderMode.sys.mjs",
 });
@@ -63,14 +65,6 @@ ChromeUtils.defineModuleGetter(
   "pktTelemetry",
   "chrome://pocket/content/pktTelemetry.jsm"
 );
-ChromeUtils.defineModuleGetter(
-  this,
-  "ExperimentAPI",
-  "resource://nimbus/ExperimentAPI.jsm"
-);
-XPCOMUtils.defineLazyModuleGetters(this, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-});
 
 const POCKET_ONSAVERECS_PREF = "extensions.pocket.onSaveRecs";
 const POCKET_ONSAVERECS_LOCLES_PREF = "extensions.pocket.onSaveRecs.locales";
diff --git a/browser/components/preferences/preferences.js b/browser/components/preferences/preferences.js
index 1d2dadc50151..8424ee387960 100644
--- a/browser/components/preferences/preferences.js
+++ b/browser/components/preferences/preferences.js
@@ -85,6 +85,7 @@ ChromeUtils.defineESModuleGetters(this, {
     "resource://gre/modules/ContextualIdentityService.sys.mjs",
   FeatureGate: "resource://featuregates/FeatureGate.sys.mjs",
   FileUtils: "resource://gre/modules/FileUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   OSKeyStore: "resource://gre/modules/OSKeyStore.sys.mjs",
   PlacesUtils: "resource://gre/modules/PlacesUtils.sys.mjs",
   QuickSuggest: "resource:///modules/QuickSuggest.sys.mjs",
@@ -106,7 +107,6 @@ XPCOMUtils.defineLazyModuleGetters(this, {
   HomePage: "resource:///modules/HomePage.jsm",
   LangPackMatcher: "resource://gre/modules/LangPackMatcher.jsm",
   LoginHelper: "resource://gre/modules/LoginHelper.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
   SelectionChangedMenulist: "resource:///modules/SelectionChangedMenulist.jsm",
   SiteDataManager: "resource:///modules/SiteDataManager.jsm",
   TransientPrefs: "resource:///modules/TransientPrefs.jsm",
diff --git a/browser/components/privatebrowsing/test/browser/head.js b/browser/components/privatebrowsing/test/browser/head.js
index f0e34ad26f8b..6bdccc631532 100644
--- a/browser/components/privatebrowsing/test/browser/head.js
+++ b/browser/components/privatebrowsing/test/browser/head.js
@@ -2,6 +2,8 @@
  * http://creativecommons.org/publicdomain/zero/1.0/ */
 
 ChromeUtils.defineESModuleGetters(this, {
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
+  ExperimentFakes: "resource://testing-common/NimbusTestUtils.sys.mjs",
   FileUtils: "resource://gre/modules/FileUtils.sys.mjs",
   PlacesTestUtils: "resource://testing-common/PlacesTestUtils.sys.mjs",
   PlacesUtils: "resource://gre/modules/PlacesUtils.sys.mjs",
@@ -10,8 +12,6 @@ ChromeUtils.defineESModuleGetters(this, {
 
 XPCOMUtils.defineLazyModuleGetters(this, {
   ASRouter: "resource://activity-stream/lib/ASRouter.jsm",
-  ExperimentAPI: "resource://nimbus/ExperimentAPI.jsm",
-  ExperimentFakes: "resource://testing-common/NimbusTestUtils.jsm",
   PanelTestProvider: "resource://activity-stream/lib/PanelTestProvider.jsm",
 });
 
diff --git a/browser/components/search/test/browser/browser_defaultPrivate_nimbus.js b/browser/components/search/test/browser/browser_defaultPrivate_nimbus.js
index 6842682db669..cc808371f9ae 100644
--- a/browser/components/search/test/browser/browser_defaultPrivate_nimbus.js
+++ b/browser/components/search/test/browser/browser_defaultPrivate_nimbus.js
@@ -2,11 +2,11 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-const { ExperimentAPI } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { ExperimentAPI } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 ChromeUtils.defineESModuleGetters(this, {
diff --git a/browser/components/search/test/browser/browser_search_nimbus_reload.js b/browser/components/search/test/browser/browser_search_nimbus_reload.js
index e4f88aae7cc7..a15391f027e2 100644
--- a/browser/components/search/test/browser/browser_search_nimbus_reload.js
+++ b/browser/components/search/test/browser/browser_search_nimbus_reload.js
@@ -3,8 +3,8 @@
 
 "use strict";
 
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 const { SearchService } = ChromeUtils.importESModule(
diff --git a/browser/components/shell/ShellService.jsm b/browser/components/shell/ShellService.jsm
index 9bdadc2415a4..efe383ec8076 100644
--- a/browser/components/shell/ShellService.jsm
+++ b/browser/components/shell/ShellService.jsm
@@ -15,15 +15,12 @@ const { XPCOMUtils } = ChromeUtils.importESModule(
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   Subprocess: "resource://gre/modules/Subprocess.sys.mjs",
   WindowsRegistry: "resource://gre/modules/WindowsRegistry.sys.mjs",
   setTimeout: "resource://gre/modules/Timer.sys.mjs",
 });
 
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-});
-
 XPCOMUtils.defineLazyServiceGetter(
   lazy,
   "XreDirProvider",
diff --git a/browser/components/shell/test/browser_doesAppNeedPin.js b/browser/components/shell/test/browser_doesAppNeedPin.js
index 1ecb6cc10852..e5dc25faf881 100644
--- a/browser/components/shell/test/browser_doesAppNeedPin.js
+++ b/browser/components/shell/test/browser_doesAppNeedPin.js
@@ -1,10 +1,10 @@
 /* Any copyright is dedicated to the Public Domain.
  * http://creativecommons.org/publicdomain/zero/1.0/ */
 
-XPCOMUtils.defineLazyModuleGetters(this, {
-  ExperimentAPI: "resource://nimbus/ExperimentAPI.jsm",
-  ExperimentFakes: "resource://testing-common/NimbusTestUtils.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
+ChromeUtils.defineESModuleGetters(this, {
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
+  ExperimentFakes: "resource://testing-common/NimbusTestUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
 });
 
 registerCleanupFunction(() => {
diff --git a/browser/components/shell/test/browser_setDefaultBrowser.js b/browser/components/shell/test/browser_setDefaultBrowser.js
index 884949ce3487..be4e152fad6b 100644
--- a/browser/components/shell/test/browser_setDefaultBrowser.js
+++ b/browser/components/shell/test/browser_setDefaultBrowser.js
@@ -2,15 +2,12 @@
  * http://creativecommons.org/publicdomain/zero/1.0/ */
 
 ChromeUtils.defineESModuleGetters(this, {
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
+  ExperimentFakes: "resource://testing-common/NimbusTestUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   sinon: "resource://testing-common/Sinon.sys.mjs",
 });
 
-XPCOMUtils.defineLazyModuleGetters(this, {
-  ExperimentAPI: "resource://nimbus/ExperimentAPI.jsm",
-  ExperimentFakes: "resource://testing-common/NimbusTestUtils.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-});
-
 const userChoiceStub = sinon
   .stub(ShellService, "setAsDefaultUserChoice")
   .resolves();
diff --git a/browser/components/shell/test/browser_setDefaultPDFHandler.js b/browser/components/shell/test/browser_setDefaultPDFHandler.js
index 2fb979f05b4a..3314a4cf210e 100644
--- a/browser/components/shell/test/browser_setDefaultPDFHandler.js
+++ b/browser/components/shell/test/browser_setDefaultPDFHandler.js
@@ -2,15 +2,12 @@
  * http://creativecommons.org/publicdomain/zero/1.0/ */
 
 ChromeUtils.defineESModuleGetters(this, {
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
+  ExperimentFakes: "resource://testing-common/NimbusTestUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   sinon: "resource://testing-common/Sinon.sys.mjs",
 });
 
-XPCOMUtils.defineLazyModuleGetters(this, {
-  ExperimentAPI: "resource://nimbus/ExperimentAPI.jsm",
-  ExperimentFakes: "resource://testing-common/NimbusTestUtils.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-});
-
 XPCOMUtils.defineLazyServiceGetter(
   this,
   "XreDirProvider",
diff --git a/browser/components/tests/browser/browser_browserGlue_upgradeDialog_trigger.js b/browser/components/tests/browser/browser_browserGlue_upgradeDialog_trigger.js
index 3abfc0a69d99..c0e1aadb8b0f 100644
--- a/browser/components/tests/browser/browser_browserGlue_upgradeDialog_trigger.js
+++ b/browser/components/tests/browser/browser_browserGlue_upgradeDialog_trigger.js
@@ -3,11 +3,11 @@ http://creativecommons.org/publicdomain/zero/1.0/ */
 
 "use strict";
 
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
-const { ExperimentAPI } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { ExperimentAPI } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
 const { OnboardingMessageProvider } = ChromeUtils.import(
   "resource://activity-stream/lib/OnboardingMessageProvider.jsm"
diff --git a/browser/components/urlbar/QuickSuggest.sys.mjs b/browser/components/urlbar/QuickSuggest.sys.mjs
index 835cefd1c642..e6b660e13192 100644
--- a/browser/components/urlbar/QuickSuggest.sys.mjs
+++ b/browser/components/urlbar/QuickSuggest.sys.mjs
@@ -7,13 +7,13 @@ import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   UrlbarPrefs: "resource:///modules/UrlbarPrefs.sys.mjs",
   UrlbarUtils: "resource:///modules/UrlbarUtils.sys.mjs",
 });
 
 XPCOMUtils.defineLazyModuleGetters(lazy, {
   BrowserWindowTracker: "resource:///modules/BrowserWindowTracker.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
 });
 
 // Quick suggest features. On init, QuickSuggest creates an instance of each and
diff --git a/browser/components/urlbar/UrlbarPrefs.sys.mjs b/browser/components/urlbar/UrlbarPrefs.sys.mjs
index 088887e662c7..304018632103 100644
--- a/browser/components/urlbar/UrlbarPrefs.sys.mjs
+++ b/browser/components/urlbar/UrlbarPrefs.sys.mjs
@@ -8,20 +8,15 @@
  * preferences, but only for variables with fallback prefs.
  */
 
-import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
-
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   Region: "resource://gre/modules/Region.sys.mjs",
   TelemetryEnvironment: "resource://gre/modules/TelemetryEnvironment.sys.mjs",
   UrlbarUtils: "resource:///modules/UrlbarUtils.sys.mjs",
 });
 
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-});
-
 const PREF_URLBAR_BRANCH = "browser.urlbar.";
 
 // Prefs are defined as [pref name, default value] or [pref name, [default
diff --git a/browser/components/urlbar/tests/UrlbarTestUtils.sys.mjs b/browser/components/urlbar/tests/UrlbarTestUtils.sys.mjs
index 7d574c394ffc..61c8bcf8ea2c 100644
--- a/browser/components/urlbar/tests/UrlbarTestUtils.sys.mjs
+++ b/browser/components/urlbar/tests/UrlbarTestUtils.sys.mjs
@@ -14,8 +14,14 @@ const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
   BrowserTestUtils: "resource://testing-common/BrowserTestUtils.sys.mjs",
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
+  ExperimentFakes: "resource://testing-common/NimbusTestUtils.sys.mjs",
+  ExperimentManager: "resource://nimbus/lib/ExperimentManager.sys.mjs",
+
   FormHistoryTestUtils:
     "resource://testing-common/FormHistoryTestUtils.sys.mjs",
+
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
   TestUtils: "resource://testing-common/TestUtils.sys.mjs",
   UrlbarController: "resource:///modules/UrlbarController.sys.mjs",
@@ -28,10 +34,6 @@ XPCOMUtils.defineLazyModuleGetters(lazy, {
   AddonTestUtils: "resource://testing-common/AddonTestUtils.jsm",
   BrowserUIUtils: "resource:///modules/BrowserUIUtils.jsm",
   BrowserWindowTracker: "resource:///modules/BrowserWindowTracker.jsm",
-  ExperimentAPI: "resource://nimbus/ExperimentAPI.jsm",
-  ExperimentFakes: "resource://testing-common/NimbusTestUtils.jsm",
-  ExperimentManager: "resource://nimbus/lib/ExperimentManager.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
 });
 
 export var UrlbarTestUtils = {
diff --git a/browser/components/urlbar/tests/browser/head.js b/browser/components/urlbar/tests/browser/head.js
index 889e485bb64e..9cd708faa1ec 100644
--- a/browser/components/urlbar/tests/browser/head.js
+++ b/browser/components/urlbar/tests/browser/head.js
@@ -8,6 +8,8 @@
 "use strict";
 
 ChromeUtils.defineESModuleGetters(this, {
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
+  ExperimentFakes: "resource://testing-common/NimbusTestUtils.sys.mjs",
   PromiseUtils: "resource://gre/modules/PromiseUtils.sys.mjs",
   PromptTestUtils: "resource://testing-common/PromptTestUtils.sys.mjs",
   ResetProfile: "resource://gre/modules/ResetProfile.sys.mjs",
@@ -24,8 +26,6 @@ ChromeUtils.defineESModuleGetters(this, {
 
 XPCOMUtils.defineLazyModuleGetters(this, {
   AboutNewTab: "resource:///modules/AboutNewTab.jsm",
-  ExperimentAPI: "resource://nimbus/ExperimentAPI.jsm",
-  ExperimentFakes: "resource://testing-common/NimbusTestUtils.jsm",
   ObjectUtils: "resource://gre/modules/ObjectUtils.jsm",
 });
 
diff --git a/browser/components/urlbar/tests/quicksuggest/QuickSuggestTestUtils.sys.mjs b/browser/components/urlbar/tests/quicksuggest/QuickSuggestTestUtils.sys.mjs
index edf04cc860cb..2d57291c7110 100644
--- a/browser/components/urlbar/tests/quicksuggest/QuickSuggestTestUtils.sys.mjs
+++ b/browser/components/urlbar/tests/quicksuggest/QuickSuggestTestUtils.sys.mjs
@@ -3,8 +3,6 @@
 
 /* eslint-disable mozilla/valid-lazy */
 
-import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
-
 import {
   CONTEXTUAL_SERVICES_PING_TYPES,
   PartnerLinkAttribution,
@@ -13,6 +11,9 @@ import {
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
+  ExperimentFakes: "resource://testing-common/NimbusTestUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   QuickSuggest: "resource:///modules/QuickSuggest.sys.mjs",
   SearchUtils: "resource://gre/modules/SearchUtils.sys.mjs",
   TelemetryTestUtils: "resource://testing-common/TelemetryTestUtils.sys.mjs",
@@ -25,12 +26,6 @@ ChromeUtils.defineESModuleGetters(lazy, {
   sinon: "resource://testing-common/Sinon.sys.mjs",
 });
 
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  ExperimentAPI: "resource://nimbus/ExperimentAPI.jsm",
-  ExperimentFakes: "resource://testing-common/NimbusTestUtils.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-});
-
 let gTestScope;
 
 // Test utils singletons need special handling. Since they are uninitialized in
diff --git a/browser/components/urlbar/tests/quicksuggest/unit/test_merinoClient.js b/browser/components/urlbar/tests/quicksuggest/unit/test_merinoClient.js
index a9b55c3dd12f..4213c5628ac0 100644
--- a/browser/components/urlbar/tests/quicksuggest/unit/test_merinoClient.js
+++ b/browser/components/urlbar/tests/quicksuggest/unit/test_merinoClient.js
@@ -7,12 +7,9 @@
 "use strict";
 
 ChromeUtils.defineESModuleGetters(this, {
+  ExperimentFakes: "resource://testing-common/NimbusTestUtils.sys.mjs",
   MerinoClient: "resource:///modules/MerinoClient.sys.mjs",
-});
-
-XPCOMUtils.defineLazyModuleGetters(this, {
-  ExperimentFakes: "resource://testing-common/NimbusTestUtils.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
 });
 
 // Set the `merino.timeoutMs` pref to a large value so that the client will not
diff --git a/browser/components/urlbar/tests/quicksuggest/unit/test_quicksuggest_migrate_v2.js b/browser/components/urlbar/tests/quicksuggest/unit/test_quicksuggest_migrate_v2.js
index 9b22a366dd4e..8f25492ef2d4 100644
--- a/browser/components/urlbar/tests/quicksuggest/unit/test_quicksuggest_migrate_v2.js
+++ b/browser/components/urlbar/tests/quicksuggest/unit/test_quicksuggest_migrate_v2.js
@@ -6,9 +6,9 @@
 
 "use strict";
 
-XPCOMUtils.defineLazyModuleGetters(this, {
-  ExperimentFakes: "resource://testing-common/NimbusTestUtils.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
+ChromeUtils.defineESModuleGetters(this, {
+  ExperimentFakes: "resource://testing-common/NimbusTestUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
 });
 
 // Expected version 2 default-branch prefs
diff --git a/services/sync/modules/engines/tabs.sys.mjs b/services/sync/modules/engines/tabs.sys.mjs
index 415b1a9e98af..2b5e7866cd5d 100644
--- a/services/sync/modules/engines/tabs.sys.mjs
+++ b/services/sync/modules/engines/tabs.sys.mjs
@@ -27,13 +27,13 @@ const FAR_FUTURE = 4102405200000; // 2100/01/01
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   PlacesUtils: "resource://gre/modules/PlacesUtils.sys.mjs",
   PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
   ReaderMode: "resource://gre/modules/ReaderMode.sys.mjs",
 });
 
 XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
   TabsStore: "resource://gre/modules/RustTabs.jsm",
 });
 
diff --git a/services/sync/tests/unit/test_tab_tracker.js b/services/sync/tests/unit/test_tab_tracker.js
index bb6401e1b21e..0d5690532f85 100644
--- a/services/sync/tests/unit/test_tab_tracker.js
+++ b/services/sync/tests/unit/test_tab_tracker.js
@@ -10,12 +10,12 @@ const { SyncScheduler } = ChromeUtils.importESModule(
   "resource://services-sync/policies.sys.mjs"
 );
 
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
-const { ExperimentAPI } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { ExperimentAPI } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
 
 var scheduler = new SyncScheduler(Service);
diff --git a/toolkit/actors/PictureInPictureChild.sys.mjs b/toolkit/actors/PictureInPictureChild.sys.mjs
index c79c5d72b667..f24a9a06c6fe 100644
--- a/toolkit/actors/PictureInPictureChild.sys.mjs
+++ b/toolkit/actors/PictureInPictureChild.sys.mjs
@@ -9,6 +9,7 @@ ChromeUtils.defineESModuleGetters(lazy, {
   ContentDOMReference: "resource://gre/modules/ContentDOMReference.sys.mjs",
   DeferredTask: "resource://gre/modules/DeferredTask.sys.mjs",
   KEYBOARD_CONTROLS: "resource://gre/modules/PictureInPictureControls.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   Rect: "resource://gre/modules/Geometry.sys.mjs",
   TOGGLE_POLICIES: "resource://gre/modules/PictureInPictureControls.sys.mjs",
   TOGGLE_POLICY_STRINGS:
@@ -19,10 +20,6 @@ const { WebVTT } = ChromeUtils.import("resource://gre/modules/vtt.jsm");
 import { setTimeout, clearTimeout } from "resource://gre/modules/Timer.sys.mjs";
 import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
 
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-});
-
 XPCOMUtils.defineLazyPreferenceGetter(
   lazy,
   "DISPLAY_TEXT_TRACKS_PREF",
diff --git a/toolkit/components/antitracking/test/browser/browser_urlQueryStringStripping_nimbus.js b/toolkit/components/antitracking/test/browser/browser_urlQueryStringStripping_nimbus.js
index 87026385e922..9ed655cf0118 100644
--- a/toolkit/components/antitracking/test/browser/browser_urlQueryStringStripping_nimbus.js
+++ b/toolkit/components/antitracking/test/browser/browser_urlQueryStringStripping_nimbus.js
@@ -10,8 +10,8 @@
  * integration works correctly in both normal and private browsing.
  */
 
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 const TEST_URI = TEST_DOMAIN + TEST_PATH + "file_stripping.html";
diff --git a/toolkit/components/backgroundtasks/BackgroundTasksUtils.sys.mjs b/toolkit/components/backgroundtasks/BackgroundTasksUtils.sys.mjs
index ef763d42eaa1..566d7a089cf1 100644
--- a/toolkit/components/backgroundtasks/BackgroundTasksUtils.sys.mjs
+++ b/toolkit/components/backgroundtasks/BackgroundTasksUtils.sys.mjs
@@ -28,13 +28,18 @@ XPCOMUtils.defineLazyServiceGetter(
   "nsIToolkitProfileService"
 );
 
+ChromeUtils.defineESModuleGetters(lazy, {
+  ExperimentManager: "resource://nimbus/lib/ExperimentManager.sys.mjs",
+
+  RemoteSettingsExperimentLoader:
+    "resource://nimbus/lib/RemoteSettingsExperimentLoader.sys.mjs",
+});
+
 XPCOMUtils.defineLazyModuleGetters(lazy, {
   ASRouter: "resource://activity-stream/lib/ASRouter.jsm",
+
   ASRouterDefaultConfig:
     "resource://activity-stream/lib/ASRouterDefaultConfig.jsm",
-  ExperimentManager: "resource://nimbus/lib/ExperimentManager.jsm",
-  RemoteSettingsExperimentLoader:
-    "resource://nimbus/lib/RemoteSettingsExperimentLoader.jsm",
 });
 
 class CannotLockProfileError extends Error {
diff --git a/toolkit/components/nimbus/ExperimentAPI.jsm b/toolkit/components/nimbus/ExperimentAPI.sys.mjs
similarity index 96%
rename from toolkit/components/nimbus/ExperimentAPI.jsm
rename to toolkit/components/nimbus/ExperimentAPI.sys.mjs
index 7a14687f6721..28fc7996f0eb 100644
--- a/toolkit/components/nimbus/ExperimentAPI.jsm
+++ b/toolkit/components/nimbus/ExperimentAPI.sys.mjs
@@ -2,30 +2,18 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-"use strict";
-
-const EXPORTED_SYMBOLS = [
-  "ExperimentAPI",
-  "NimbusFeatures",
-  "_ExperimentFeature",
-];
-
-const { XPCOMUtils } = ChromeUtils.importESModule(
-  "resource://gre/modules/XPCOMUtils.sys.mjs"
-);
-const { AppConstants } = ChromeUtils.importESModule(
-  "resource://gre/modules/AppConstants.sys.mjs"
-);
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
+import { AppConstants } from "resource://gre/modules/AppConstants.sys.mjs";
 
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
+  ExperimentManager: "resource://nimbus/lib/ExperimentManager.sys.mjs",
+  ExperimentStore: "resource://nimbus/lib/ExperimentStore.sys.mjs",
   RemoteSettings: "resource://services-settings/remote-settings.sys.mjs",
 });
 
 XPCOMUtils.defineLazyModuleGetters(lazy, {
-  ExperimentStore: "resource://nimbus/lib/ExperimentStore.jsm",
-  ExperimentManager: "resource://nimbus/lib/ExperimentManager.jsm",
   FeatureManifest: "resource://nimbus/FeatureManifest.js",
 });
 
@@ -85,7 +73,7 @@ const experimentBranchAccessor = {
   },
 };
 
-const ExperimentAPI = {
+export const ExperimentAPI = {
   /**
    * @returns {Promise} Resolves when the API has synchronized to the main store
    */
@@ -305,14 +293,15 @@ const ExperimentAPI = {
  * Singleton that holds lazy references to _ExperimentFeature instances
  * defined by the FeatureManifest
  */
-const NimbusFeatures = {};
+export const NimbusFeatures = {};
+
 for (let feature in lazy.FeatureManifest) {
   XPCOMUtils.defineLazyGetter(NimbusFeatures, feature, () => {
     return new _ExperimentFeature(feature);
   });
 }
 
-class _ExperimentFeature {
+export class _ExperimentFeature {
   constructor(featureId, manifest) {
     this.featureId = featureId;
     this.prefGetters = {};
diff --git a/toolkit/components/nimbus/jar.mn b/toolkit/components/nimbus/jar.mn
index 19e2ede5c9ba..8be3ce7c0c04 100644
--- a/toolkit/components/nimbus/jar.mn
+++ b/toolkit/components/nimbus/jar.mn
@@ -4,8 +4,8 @@
 
 toolkit.jar:
 % resource nimbus %res/nimbus/
-  res/nimbus/lib/ (./lib/*.jsm)
-  res/nimbus/ExperimentAPI.jsm (./ExperimentAPI.jsm)
+  res/nimbus/lib/ (./lib/*.sys.mjs)
+  res/nimbus/ExperimentAPI.sys.mjs (./ExperimentAPI.sys.mjs)
   res/nimbus/FeatureManifest.js (FeatureManifest.js)
   res/nimbus/schemas/NimbusEnrollment.schema.json (./schemas/NimbusEnrollment.schema.json)
   res/nimbus/schemas/NimbusExperiment.schema.json (./schemas/NimbusExperiment.schema.json)
diff --git a/toolkit/components/nimbus/lib/ExperimentManager.jsm b/toolkit/components/nimbus/lib/ExperimentManager.sys.mjs
similarity index 99%
rename from toolkit/components/nimbus/lib/ExperimentManager.jsm
rename to toolkit/components/nimbus/lib/ExperimentManager.sys.mjs
index de99dd013649..2b5f7a5dae4d 100644
--- a/toolkit/components/nimbus/lib/ExperimentManager.jsm
+++ b/toolkit/components/nimbus/lib/ExperimentManager.sys.mjs
@@ -2,26 +2,20 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-"use strict";
-
-const EXPORTED_SYMBOLS = ["ExperimentManager", "_ExperimentManager"];
-
-const { XPCOMUtils } = ChromeUtils.importESModule(
-  "resource://gre/modules/XPCOMUtils.sys.mjs"
-);
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
 
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
+  ExperimentStore: "resource://nimbus/lib/ExperimentStore.sys.mjs",
   FirstStartup: "resource://gre/modules/FirstStartup.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   Sampling: "resource://gre/modules/components-utils/Sampling.sys.mjs",
   TelemetryEnvironment: "resource://gre/modules/TelemetryEnvironment.sys.mjs",
 });
 
 XPCOMUtils.defineLazyModuleGetters(lazy, {
   ClientEnvironment: "resource://normandy/lib/ClientEnvironment.jsm",
-  ExperimentStore: "resource://nimbus/lib/ExperimentStore.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
   NormandyUtils: "resource://normandy/lib/NormandyUtils.jsm",
   TelemetryEvents: "resource://normandy/lib/TelemetryEvents.jsm",
   PrefUtils: "resource://normandy/lib/PrefUtils.jsm",
@@ -66,7 +60,7 @@ function getFeatureFromBranch(branch, featureId) {
  * A module for processes Experiment recipes, choosing and storing enrollment state,
  * and sending experiment-related Telemetry.
  */
-class _ExperimentManager {
+export class _ExperimentManager {
   constructor({ id = "experimentmanager", store } = {}) {
     this.id = id;
     this.store = store || new lazy.ExperimentStore();
@@ -1273,4 +1267,4 @@ class _ExperimentManager {
   }
 }
 
-const ExperimentManager = new _ExperimentManager();
+export const ExperimentManager = new _ExperimentManager();
diff --git a/toolkit/components/nimbus/lib/ExperimentStore.jsm b/toolkit/components/nimbus/lib/ExperimentStore.sys.mjs
similarity index 98%
rename from toolkit/components/nimbus/lib/ExperimentStore.jsm
rename to toolkit/components/nimbus/lib/ExperimentStore.sys.mjs
index 002515d05359..af6cdaab29fb 100644
--- a/toolkit/components/nimbus/lib/ExperimentStore.jsm
+++ b/toolkit/components/nimbus/lib/ExperimentStore.sys.mjs
@@ -2,16 +2,10 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-"use strict";
+import { SharedDataMap } from "resource://nimbus/lib/SharedDataMap.sys.mjs";
 
-const EXPORTED_SYMBOLS = ["ExperimentStore"];
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
 
-const { SharedDataMap } = ChromeUtils.import(
-  "resource://nimbus/lib/SharedDataMap.jsm"
-);
-const { XPCOMUtils } = ChromeUtils.importESModule(
-  "resource://gre/modules/XPCOMUtils.sys.mjs"
-);
 const lazy = {};
 XPCOMUtils.defineLazyModuleGetters(lazy, {
   FeatureManifest: "resource://nimbus/FeatureManifest.js",
@@ -233,7 +227,7 @@ function featuresCompat(branch) {
   return features;
 }
 
-class ExperimentStore extends SharedDataMap {
+export class ExperimentStore extends SharedDataMap {
   static SYNC_DATA_PREF_BRANCH = SYNC_DATA_PREF_BRANCH;
   static SYNC_DEFAULTS_PREF_BRANCH = SYNC_DEFAULTS_PREF_BRANCH;
 
diff --git a/toolkit/components/nimbus/lib/RemoteSettingsExperimentLoader.jsm b/toolkit/components/nimbus/lib/RemoteSettingsExperimentLoader.sys.mjs
similarity index 97%
rename from toolkit/components/nimbus/lib/RemoteSettingsExperimentLoader.jsm
rename to toolkit/components/nimbus/lib/RemoteSettingsExperimentLoader.sys.mjs
index 44b977ff227a..07ad0c2ba8bc 100644
--- a/toolkit/components/nimbus/lib/RemoteSettingsExperimentLoader.jsm
+++ b/toolkit/components/nimbus/lib/RemoteSettingsExperimentLoader.sys.mjs
@@ -2,31 +2,21 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-"use strict";
-
-const EXPORTED_SYMBOLS = [
-  "_RemoteSettingsExperimentLoader",
-  "RemoteSettingsExperimentLoader",
-  "EnrollmentsContext",
-];
-
-const { XPCOMUtils } = ChromeUtils.importESModule(
-  "resource://gre/modules/XPCOMUtils.sys.mjs"
-);
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
 
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
+  ExperimentManager: "resource://nimbus/lib/ExperimentManager.sys.mjs",
   JsonSchema: "resource://gre/modules/JsonSchema.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   RemoteSettings: "resource://services-settings/remote-settings.sys.mjs",
   TargetingContext: "resource://messaging-system/targeting/Targeting.sys.mjs",
 });
 
 XPCOMUtils.defineLazyModuleGetters(lazy, {
   ASRouterTargeting: "resource://activity-stream/lib/ASRouterTargeting.jsm",
-  ExperimentManager: "resource://nimbus/lib/ExperimentManager.jsm",
   CleanupManager: "resource://normandy/lib/CleanupManager.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
 });
 
 XPCOMUtils.defineLazyGetter(lazy, "log", () => {
@@ -86,7 +76,7 @@ const SCHEMAS = {
   },
 };
 
-class _RemoteSettingsExperimentLoader {
+export class _RemoteSettingsExperimentLoader {
   constructor() {
     // Has the timer been set?
     this._initialized = false;
@@ -368,7 +358,7 @@ class _RemoteSettingsExperimentLoader {
   }
 }
 
-class EnrollmentsContext {
+export class EnrollmentsContext {
   constructor(
     experimentManager,
     recipeValidator,
@@ -666,4 +656,4 @@ class EnrollmentsContext {
   }
 }
 
-const RemoteSettingsExperimentLoader = new _RemoteSettingsExperimentLoader();
+export const RemoteSettingsExperimentLoader = new _RemoteSettingsExperimentLoader();
diff --git a/toolkit/components/nimbus/lib/SharedDataMap.jsm b/toolkit/components/nimbus/lib/SharedDataMap.sys.mjs
similarity index 93%
rename from toolkit/components/nimbus/lib/SharedDataMap.jsm
rename to toolkit/components/nimbus/lib/SharedDataMap.sys.mjs
index 7817f5d6259d..f7d38f32ea0c 100644
--- a/toolkit/components/nimbus/lib/SharedDataMap.jsm
+++ b/toolkit/components/nimbus/lib/SharedDataMap.sys.mjs
@@ -2,13 +2,9 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-"use strict";
+import { EventEmitter } from "resource://gre/modules/EventEmitter.sys.mjs";
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
 
-const EXPORTED_SYMBOLS = ["SharedDataMap"];
-
-const { EventEmitter } = ChromeUtils.importESModule(
-  "resource://gre/modules/EventEmitter.sys.mjs"
-);
 const lazy = {};
 ChromeUtils.defineESModuleGetters(lazy, {
   JSONFile: "resource://gre/modules/JSONFile.sys.mjs",
@@ -18,11 +14,7 @@ ChromeUtils.defineESModuleGetters(lazy, {
 const IS_MAIN_PROCESS =
   Services.appinfo.processType === Services.appinfo.PROCESS_TYPE_DEFAULT;
 
-const { XPCOMUtils } = ChromeUtils.importESModule(
-  "resource://gre/modules/XPCOMUtils.sys.mjs"
-);
-
-class SharedDataMap extends EventEmitter {
+export class SharedDataMap extends EventEmitter {
   constructor(sharedDataKey, options = { isParent: IS_MAIN_PROCESS }) {
     super();
 
diff --git a/toolkit/components/nimbus/moz.build b/toolkit/components/nimbus/moz.build
index 8f1ada80cf9e..c04180030315 100644
--- a/toolkit/components/nimbus/moz.build
+++ b/toolkit/components/nimbus/moz.build
@@ -29,7 +29,7 @@ XPCSHELL_TESTS_MANIFESTS += ["test/unit/xpcshell.ini"]
 SPHINX_TREES["docs"] = "docs"
 
 TESTING_JS_MODULES += [
-    "test/NimbusTestUtils.jsm",
+    "test/NimbusTestUtils.sys.mjs",
 ]
 
 GeneratedFile(
diff --git a/toolkit/components/nimbus/test/NimbusTestUtils.jsm b/toolkit/components/nimbus/test/NimbusTestUtils.sys.mjs
similarity index 94%
rename from toolkit/components/nimbus/test/NimbusTestUtils.jsm
rename to toolkit/components/nimbus/test/NimbusTestUtils.sys.mjs
index 9732f42656f2..2549cdf566f7 100644
--- a/toolkit/components/nimbus/test/NimbusTestUtils.jsm
+++ b/toolkit/components/nimbus/test/NimbusTestUtils.sys.mjs
@@ -2,34 +2,24 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-"use strict";
-
-const { XPCOMUtils } = ChromeUtils.importESModule(
-  "resource://gre/modules/XPCOMUtils.sys.mjs"
-);
-
-const { ExperimentStore } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentStore.jsm"
-);
-
-const { FileTestUtils } = ChromeUtils.importESModule(
-  "resource://testing-common/FileTestUtils.sys.mjs"
-);
+import { ExperimentStore } from "resource://nimbus/lib/ExperimentStore.sys.mjs";
+import { FileTestUtils } from "resource://testing-common/FileTestUtils.sys.mjs";
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
 
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
+  ExperimentManager: "resource://nimbus/lib/ExperimentManager.sys.mjs",
   JsonSchema: "resource://gre/modules/JsonSchema.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
+  _ExperimentManager: "resource://nimbus/lib/ExperimentManager.sys.mjs",
+  _RemoteSettingsExperimentLoader:
+    "resource://nimbus/lib/RemoteSettingsExperimentLoader.sys.mjs",
   sinon: "resource://testing-common/Sinon.sys.mjs",
 });
 
 XPCOMUtils.defineLazyModuleGetters(lazy, {
-  _ExperimentManager: "resource://nimbus/lib/ExperimentManager.jsm",
-  ExperimentManager: "resource://nimbus/lib/ExperimentManager.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
   NormandyUtils: "resource://normandy/lib/NormandyUtils.jsm",
-  _RemoteSettingsExperimentLoader:
-    "resource://nimbus/lib/RemoteSettingsExperimentLoader.jsm",
   FeatureManifest: "resource://nimbus/FeatureManifest.js",
 });
 
@@ -46,9 +36,7 @@ async function fetchSchema(url) {
   return schema;
 }
 
-const EXPORTED_SYMBOLS = ["ExperimentTestUtils", "ExperimentFakes"];
-
-const ExperimentTestUtils = {
+export const ExperimentTestUtils = {
   _validateSchema(schema, value, errorMsg) {
     const result = lazy.JsonSchema.validate(value, schema, {
       shortCircuit: false,
@@ -171,7 +159,7 @@ const ExperimentTestUtils = {
   },
 };
 
-const ExperimentFakes = {
+export const ExperimentFakes = {
   manager(store) {
     let sandbox = lazy.sinon.createSandbox();
     let manager = new lazy._ExperimentManager({ store: store || this.store() });
diff --git a/toolkit/components/nimbus/test/browser/browser_experiment_evaluate_jexl.js b/toolkit/components/nimbus/test/browser/browser_experiment_evaluate_jexl.js
index a3c738369234..e811c90e0a18 100644
--- a/toolkit/components/nimbus/test/browser/browser_experiment_evaluate_jexl.js
+++ b/toolkit/components/nimbus/test/browser/browser_experiment_evaluate_jexl.js
@@ -3,14 +3,14 @@
 const {
   EnrollmentsContext,
   RemoteSettingsExperimentLoader,
-} = ChromeUtils.import(
-  "resource://nimbus/lib/RemoteSettingsExperimentLoader.jsm"
+} = ChromeUtils.importESModule(
+  "resource://nimbus/lib/RemoteSettingsExperimentLoader.sys.mjs"
 );
-const { ExperimentManager } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentManager.jsm"
+const { ExperimentManager } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/ExperimentManager.sys.mjs"
 );
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 add_setup(async function setup() {
diff --git a/toolkit/components/nimbus/test/browser/browser_experiment_single_feature_enrollment.js b/toolkit/components/nimbus/test/browser/browser_experiment_single_feature_enrollment.js
index f4b392f03ec9..ac20ff8b7a40 100644
--- a/toolkit/components/nimbus/test/browser/browser_experiment_single_feature_enrollment.js
+++ b/toolkit/components/nimbus/test/browser/browser_experiment_single_feature_enrollment.js
@@ -3,11 +3,11 @@
 
 "use strict";
 
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
-const { ExperimentAPI } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { ExperimentAPI } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
 
 const SINGLE_FEATURE_RECIPE = {
diff --git a/toolkit/components/nimbus/test/browser/browser_experimentstore_load.js b/toolkit/components/nimbus/test/browser/browser_experimentstore_load.js
index 92993a97719c..a6f526e764ec 100644
--- a/toolkit/components/nimbus/test/browser/browser_experimentstore_load.js
+++ b/toolkit/components/nimbus/test/browser/browser_experimentstore_load.js
@@ -3,14 +3,14 @@
 
 "use strict";
 
-const { ExperimentStore } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentStore.jsm"
+const { ExperimentStore } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/ExperimentStore.sys.mjs"
 );
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
-const { ExperimentFeatures } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { ExperimentFeatures } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
 ChromeUtils.defineESModuleGetters(this, {
   JSONFile: "resource://gre/modules/JSONFile.sys.mjs",
diff --git a/toolkit/components/nimbus/test/browser/browser_experimentstore_load_single_feature.js b/toolkit/components/nimbus/test/browser/browser_experimentstore_load_single_feature.js
index 60be5f008e2d..7e9a19e21d07 100644
--- a/toolkit/components/nimbus/test/browser/browser_experimentstore_load_single_feature.js
+++ b/toolkit/components/nimbus/test/browser/browser_experimentstore_load_single_feature.js
@@ -3,14 +3,14 @@
 
 "use strict";
 
-const { ExperimentStore } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentStore.jsm"
+const { ExperimentStore } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/ExperimentStore.sys.mjs"
 );
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
-const { ExperimentAPI } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { ExperimentAPI } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
 ChromeUtils.defineESModuleGetters(this, {
   JSONFile: "resource://gre/modules/JSONFile.sys.mjs",
diff --git a/toolkit/components/nimbus/test/browser/browser_nimbus_telemetry.js b/toolkit/components/nimbus/test/browser/browser_nimbus_telemetry.js
index 9197a78dad02..78def6df89c8 100644
--- a/toolkit/components/nimbus/test/browser/browser_nimbus_telemetry.js
+++ b/toolkit/components/nimbus/test/browser/browser_nimbus_telemetry.js
@@ -3,12 +3,12 @@
 const {
   ExperimentAPI,
   _ExperimentFeature: ExperimentFeature,
-} = ChromeUtils.import("resource://nimbus/ExperimentAPI.jsm");
-const { ExperimentManager } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentManager.jsm"
+} = ChromeUtils.importESModule("resource://nimbus/ExperimentAPI.sys.mjs");
+const { ExperimentManager } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/ExperimentManager.sys.mjs"
 );
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 const { TelemetryTestUtils } = ChromeUtils.importESModule(
   "resource://testing-common/TelemetryTestUtils.sys.mjs"
diff --git a/toolkit/components/nimbus/test/browser/browser_prefs.js b/toolkit/components/nimbus/test/browser/browser_prefs.js
index 803f5deb3c8e..6c38d164283f 100644
--- a/toolkit/components/nimbus/test/browser/browser_prefs.js
+++ b/toolkit/components/nimbus/test/browser/browser_prefs.js
@@ -3,14 +3,14 @@
 
 "use strict";
 
-const { ExperimentAPI } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { ExperimentAPI } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
-const { ExperimentManager } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentManager.jsm"
+const { ExperimentManager } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/ExperimentManager.sys.mjs"
 );
 
 const EXPERIMENT_VALUE = "experiment-value";
diff --git a/toolkit/components/nimbus/test/browser/browser_remotesettings_experiment_enroll.js b/toolkit/components/nimbus/test/browser/browser_remotesettings_experiment_enroll.js
index 32a0a5b49b21..2f699b932f14 100644
--- a/toolkit/components/nimbus/test/browser/browser_remotesettings_experiment_enroll.js
+++ b/toolkit/components/nimbus/test/browser/browser_remotesettings_experiment_enroll.js
@@ -3,17 +3,17 @@
 const { RemoteSettings } = ChromeUtils.importESModule(
   "resource://services-settings/remote-settings.sys.mjs"
 );
-const { RemoteSettingsExperimentLoader } = ChromeUtils.import(
-  "resource://nimbus/lib/RemoteSettingsExperimentLoader.jsm"
+const { RemoteSettingsExperimentLoader } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/RemoteSettingsExperimentLoader.sys.mjs"
 );
-const { ExperimentAPI } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { ExperimentAPI } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
-const { ExperimentManager } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentManager.jsm"
+const { ExperimentManager } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/ExperimentManager.sys.mjs"
 );
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 let rsClient;
diff --git a/toolkit/components/nimbus/test/browser/browser_remotesettingsexperimentloader_force_enrollment.js b/toolkit/components/nimbus/test/browser/browser_remotesettingsexperimentloader_force_enrollment.js
index 64f223fd6def..7c501b22fafd 100644
--- a/toolkit/components/nimbus/test/browser/browser_remotesettingsexperimentloader_force_enrollment.js
+++ b/toolkit/components/nimbus/test/browser/browser_remotesettingsexperimentloader_force_enrollment.js
@@ -5,14 +5,14 @@
 const { RemoteSettings } = ChromeUtils.importESModule(
   "resource://services-settings/remote-settings.sys.mjs"
 );
-const { RemoteSettingsExperimentLoader } = ChromeUtils.import(
-  "resource://nimbus/lib/RemoteSettingsExperimentLoader.jsm"
+const { RemoteSettingsExperimentLoader } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/RemoteSettingsExperimentLoader.sys.mjs"
 );
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
-const { ExperimentManager } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentManager.jsm"
+const { ExperimentManager } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/ExperimentManager.sys.mjs"
 );
 
 async function setup(recipes) {
diff --git a/toolkit/components/nimbus/test/browser/browser_remotesettingsexperimentloader_init.js b/toolkit/components/nimbus/test/browser/browser_remotesettingsexperimentloader_init.js
index 8f9c91b81c85..f80fb7dfa51a 100644
--- a/toolkit/components/nimbus/test/browser/browser_remotesettingsexperimentloader_init.js
+++ b/toolkit/components/nimbus/test/browser/browser_remotesettingsexperimentloader_init.js
@@ -3,14 +3,14 @@
 
 "use strict";
 
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
-const { ExperimentManager } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentManager.jsm"
+const { ExperimentManager } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/ExperimentManager.sys.mjs"
 );
-const { ExperimentAPI } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { ExperimentAPI } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
 
 function getRecipe(slug) {
diff --git a/toolkit/components/nimbus/test/browser/browser_remotesettingsexperimentloader_remote_defaults.js b/toolkit/components/nimbus/test/browser/browser_remotesettingsexperimentloader_remote_defaults.js
index 6fc22ee156f6..e88c551c0567 100644
--- a/toolkit/components/nimbus/test/browser/browser_remotesettingsexperimentloader_remote_defaults.js
+++ b/toolkit/components/nimbus/test/browser/browser_remotesettingsexperimentloader_remote_defaults.js
@@ -10,15 +10,15 @@ const {
   _ExperimentFeature: ExperimentFeature,
 
   ExperimentAPI,
-} = ChromeUtils.import("resource://nimbus/ExperimentAPI.jsm");
-const { ExperimentTestUtils } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+} = ChromeUtils.importESModule("resource://nimbus/ExperimentAPI.sys.mjs");
+const { ExperimentTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
-const { ExperimentManager } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentManager.jsm"
+const { ExperimentManager } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/ExperimentManager.sys.mjs"
 );
-const { RemoteSettingsExperimentLoader } = ChromeUtils.import(
-  "resource://nimbus/lib/RemoteSettingsExperimentLoader.jsm"
+const { RemoteSettingsExperimentLoader } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/RemoteSettingsExperimentLoader.sys.mjs"
 );
 
 const FOO_FAKE_FEATURE_MANIFEST = {
diff --git a/toolkit/components/nimbus/test/browser/head.js b/toolkit/components/nimbus/test/browser/head.js
index a69bb5541daf..dfcb149f7df1 100644
--- a/toolkit/components/nimbus/test/browser/head.js
+++ b/toolkit/components/nimbus/test/browser/head.js
@@ -8,10 +8,10 @@ const { sinon } = ChromeUtils.importESModule(
   "resource://testing-common/Sinon.sys.mjs"
 );
 
-XPCOMUtils.defineLazyModuleGetters(this, {
-  ExperimentManager: "resource://nimbus/lib/ExperimentManager.jsm",
-  ExperimentTestUtils: "resource://testing-common/NimbusTestUtils.jsm",
-  ExperimentFakes: "resource://testing-common/NimbusTestUtils.jsm",
+ChromeUtils.defineESModuleGetters(this, {
+  ExperimentManager: "resource://nimbus/lib/ExperimentManager.sys.mjs",
+  ExperimentTestUtils: "resource://testing-common/NimbusTestUtils.sys.mjs",
+  ExperimentFakes: "resource://testing-common/NimbusTestUtils.sys.mjs",
 });
 
 add_setup(function() {
diff --git a/toolkit/components/nimbus/test/unit/head.js b/toolkit/components/nimbus/test/unit/head.js
index 814ec9c588ff..5a8c4ceddd14 100644
--- a/toolkit/components/nimbus/test/unit/head.js
+++ b/toolkit/components/nimbus/test/unit/head.js
@@ -7,7 +7,7 @@ const { sinon } = ChromeUtils.importESModule(
 const { XPCOMUtils } = ChromeUtils.importESModule(
   "resource://gre/modules/XPCOMUtils.sys.mjs"
 );
-XPCOMUtils.defineLazyModuleGetters(this, {
-  ExperimentFakes: "resource://testing-common/NimbusTestUtils.jsm",
-  ExperimentTestUtils: "resource://testing-common/NimbusTestUtils.jsm",
+ChromeUtils.defineESModuleGetters(this, {
+  ExperimentFakes: "resource://testing-common/NimbusTestUtils.sys.mjs",
+  ExperimentTestUtils: "resource://testing-common/NimbusTestUtils.sys.mjs",
 });
diff --git a/toolkit/components/nimbus/test/unit/test_ExperimentAPI.js b/toolkit/components/nimbus/test/unit/test_ExperimentAPI.js
index 336f14f837ba..722011f5b825 100644
--- a/toolkit/components/nimbus/test/unit/test_ExperimentAPI.js
+++ b/toolkit/components/nimbus/test/unit/test_ExperimentAPI.js
@@ -1,10 +1,10 @@
 "use strict";
 
-const { ExperimentAPI } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { ExperimentAPI } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 const { TestUtils } = ChromeUtils.importESModule(
   "resource://testing-common/TestUtils.sys.mjs"
diff --git a/toolkit/components/nimbus/test/unit/test_ExperimentAPI_ExperimentFeature.js b/toolkit/components/nimbus/test/unit/test_ExperimentAPI_ExperimentFeature.js
index c2116199ef56..6df30e4f30d7 100644
--- a/toolkit/components/nimbus/test/unit/test_ExperimentAPI_ExperimentFeature.js
+++ b/toolkit/components/nimbus/test/unit/test_ExperimentAPI_ExperimentFeature.js
@@ -3,9 +3,9 @@
 const {
   ExperimentAPI,
   _ExperimentFeature: ExperimentFeature,
-} = ChromeUtils.import("resource://nimbus/ExperimentAPI.jsm");
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+} = ChromeUtils.importESModule("resource://nimbus/ExperimentAPI.sys.mjs");
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 async function setupForExperimentFeature() {
diff --git a/toolkit/components/nimbus/test/unit/test_ExperimentAPI_ExperimentFeature_getAllVariables.js b/toolkit/components/nimbus/test/unit/test_ExperimentAPI_ExperimentFeature_getAllVariables.js
index b29d84c93786..3c57b11a8388 100644
--- a/toolkit/components/nimbus/test/unit/test_ExperimentAPI_ExperimentFeature_getAllVariables.js
+++ b/toolkit/components/nimbus/test/unit/test_ExperimentAPI_ExperimentFeature_getAllVariables.js
@@ -3,9 +3,9 @@
 const {
   ExperimentAPI,
   _ExperimentFeature: ExperimentFeature,
-} = ChromeUtils.import("resource://nimbus/ExperimentAPI.jsm");
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+} = ChromeUtils.importESModule("resource://nimbus/ExperimentAPI.sys.mjs");
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 const { cleanupStorePrefCache } = ExperimentFakes;
diff --git a/toolkit/components/nimbus/test/unit/test_ExperimentAPI_ExperimentFeature_getVariable.js b/toolkit/components/nimbus/test/unit/test_ExperimentAPI_ExperimentFeature_getVariable.js
index 4fbbb3792fb8..27e95c574ac2 100644
--- a/toolkit/components/nimbus/test/unit/test_ExperimentAPI_ExperimentFeature_getVariable.js
+++ b/toolkit/components/nimbus/test/unit/test_ExperimentAPI_ExperimentFeature_getVariable.js
@@ -3,7 +3,7 @@
 const {
   ExperimentAPI,
   _ExperimentFeature: ExperimentFeature,
-} = ChromeUtils.import("resource://nimbus/ExperimentAPI.jsm");
+} = ChromeUtils.importESModule("resource://nimbus/ExperimentAPI.sys.mjs");
 const { AppConstants } = ChromeUtils.importESModule(
   "resource://gre/modules/AppConstants.sys.mjs"
 );
diff --git a/toolkit/components/nimbus/test/unit/test_ExperimentAPI_NimbusFeatures.js b/toolkit/components/nimbus/test/unit/test_ExperimentAPI_NimbusFeatures.js
index 7c4de4ec42ef..99a70a3e91c1 100644
--- a/toolkit/components/nimbus/test/unit/test_ExperimentAPI_NimbusFeatures.js
+++ b/toolkit/components/nimbus/test/unit/test_ExperimentAPI_NimbusFeatures.js
@@ -3,7 +3,7 @@
 const {
   ExperimentAPI,
   _ExperimentFeature: ExperimentFeature,
-} = ChromeUtils.import("resource://nimbus/ExperimentAPI.jsm");
+} = ChromeUtils.importESModule("resource://nimbus/ExperimentAPI.sys.mjs");
 
 const { JsonSchema } = ChromeUtils.importESModule(
   "resource://gre/modules/JsonSchema.sys.mjs"
diff --git a/toolkit/components/nimbus/test/unit/test_ExperimentManager_context.js b/toolkit/components/nimbus/test/unit/test_ExperimentManager_context.js
index 5194d92bb665..b8cdb3afc924 100644
--- a/toolkit/components/nimbus/test/unit/test_ExperimentManager_context.js
+++ b/toolkit/components/nimbus/test/unit/test_ExperimentManager_context.js
@@ -1,7 +1,7 @@
 "use strict";
 
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 const { FirstStartup } = ChromeUtils.importESModule(
diff --git a/toolkit/components/nimbus/test/unit/test_ExperimentManager_enroll.js b/toolkit/components/nimbus/test/unit/test_ExperimentManager_enroll.js
index 8ab9573bb192..95c6ae893e61 100644
--- a/toolkit/components/nimbus/test/unit/test_ExperimentManager_enroll.js
+++ b/toolkit/components/nimbus/test/unit/test_ExperimentManager_enroll.js
@@ -11,8 +11,8 @@ const { ClientEnvironment } = ChromeUtils.import(
 );
 const { cleanupStorePrefCache } = ExperimentFakes;
 
-const { ExperimentStore } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentStore.jsm"
+const { ExperimentStore } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/ExperimentStore.sys.mjs"
 );
 const { TelemetryEnvironment } = ChromeUtils.importESModule(
   "resource://gre/modules/TelemetryEnvironment.sys.mjs"
diff --git a/toolkit/components/nimbus/test/unit/test_ExperimentManager_generateTestIds.js b/toolkit/components/nimbus/test/unit/test_ExperimentManager_generateTestIds.js
index 17b34dc199ac..87c50f61c8d4 100644
--- a/toolkit/components/nimbus/test/unit/test_ExperimentManager_generateTestIds.js
+++ b/toolkit/components/nimbus/test/unit/test_ExperimentManager_generateTestIds.js
@@ -1,6 +1,6 @@
 "use strict";
-const { ExperimentManager } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentManager.jsm"
+const { ExperimentManager } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/ExperimentManager.sys.mjs"
 );
 
 const TEST_CONFIG = {
diff --git a/toolkit/components/nimbus/test/unit/test_ExperimentManager_prefs.js b/toolkit/components/nimbus/test/unit/test_ExperimentManager_prefs.js
index 5e1d2d24dc7f..a980f217fea1 100644
--- a/toolkit/components/nimbus/test/unit/test_ExperimentManager_prefs.js
+++ b/toolkit/components/nimbus/test/unit/test_ExperimentManager_prefs.js
@@ -4,7 +4,7 @@
 const {
   _ExperimentFeature: ExperimentFeature,
   NimbusFeatures,
-} = ChromeUtils.import("resource://nimbus/ExperimentAPI.jsm");
+} = ChromeUtils.importESModule("resource://nimbus/ExperimentAPI.sys.mjs");
 
 const { PrefUtils } = ChromeUtils.import(
   "resource://normandy/lib/PrefUtils.jsm"
diff --git a/toolkit/components/nimbus/test/unit/test_ExperimentStore.js b/toolkit/components/nimbus/test/unit/test_ExperimentStore.js
index e370b0daee36..bb6e7893467a 100644
--- a/toolkit/components/nimbus/test/unit/test_ExperimentStore.js
+++ b/toolkit/components/nimbus/test/unit/test_ExperimentStore.js
@@ -1,7 +1,7 @@
 "use strict";
 
-const { ExperimentStore } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentStore.jsm"
+const { ExperimentStore } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/ExperimentStore.sys.mjs"
 );
 const { FeatureManifest } = ChromeUtils.import(
   "resource://nimbus/FeatureManifest.js"
diff --git a/toolkit/components/nimbus/test/unit/test_NimbusTestUtils.js b/toolkit/components/nimbus/test/unit/test_NimbusTestUtils.js
index 13eb2ba80a59..1815dcfdd8bb 100644
--- a/toolkit/components/nimbus/test/unit/test_NimbusTestUtils.js
+++ b/toolkit/components/nimbus/test/unit/test_NimbusTestUtils.js
@@ -1,7 +1,7 @@
 "use strict";
 
-const { ExperimentFakes, ExperimentTestUtils } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes, ExperimentTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 add_task(async function test_recipe_fake_validates() {
diff --git a/toolkit/components/nimbus/test/unit/test_RemoteSettingsExperimentLoader.js b/toolkit/components/nimbus/test/unit/test_RemoteSettingsExperimentLoader.js
index f3944a89e01d..4f54c1f6707b 100644
--- a/toolkit/components/nimbus/test/unit/test_RemoteSettingsExperimentLoader.js
+++ b/toolkit/components/nimbus/test/unit/test_RemoteSettingsExperimentLoader.js
@@ -1,16 +1,16 @@
 "use strict";
 
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
-const { ExperimentManager } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentManager.jsm"
+const { ExperimentManager } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/ExperimentManager.sys.mjs"
 );
 const {
   RemoteSettingsExperimentLoader,
   EnrollmentsContext,
-} = ChromeUtils.import(
-  "resource://nimbus/lib/RemoteSettingsExperimentLoader.jsm"
+} = ChromeUtils.importESModule(
+  "resource://nimbus/lib/RemoteSettingsExperimentLoader.sys.mjs"
 );
 const { TestUtils } = ChromeUtils.importESModule(
   "resource://testing-common/TestUtils.sys.mjs"
diff --git a/toolkit/components/nimbus/test/unit/test_RemoteSettingsExperimentLoader_updateRecipes.js b/toolkit/components/nimbus/test/unit/test_RemoteSettingsExperimentLoader_updateRecipes.js
index 31fcb27841ec..c20a448a80b9 100644
--- a/toolkit/components/nimbus/test/unit/test_RemoteSettingsExperimentLoader_updateRecipes.js
+++ b/toolkit/components/nimbus/test/unit/test_RemoteSettingsExperimentLoader_updateRecipes.js
@@ -1,16 +1,16 @@
 "use strict";
 
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 const { FirstStartup } = ChromeUtils.importESModule(
   "resource://gre/modules/FirstStartup.sys.mjs"
 );
-const { NimbusFeatures } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { NimbusFeatures } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
-const { EnrollmentsContext } = ChromeUtils.import(
-  "resource://nimbus/lib/RemoteSettingsExperimentLoader.jsm"
+const { EnrollmentsContext } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/RemoteSettingsExperimentLoader.sys.mjs"
 );
 const { PanelTestProvider } = ChromeUtils.import(
   "resource://activity-stream/lib/PanelTestProvider.jsm"
diff --git a/toolkit/components/nimbus/test/unit/test_SharedDataMap.js b/toolkit/components/nimbus/test/unit/test_SharedDataMap.js
index 06abad981d38..6186b41a4089 100644
--- a/toolkit/components/nimbus/test/unit/test_SharedDataMap.js
+++ b/toolkit/components/nimbus/test/unit/test_SharedDataMap.js
@@ -1,5 +1,5 @@
-const { SharedDataMap } = ChromeUtils.import(
-  "resource://nimbus/lib/SharedDataMap.jsm"
+const { SharedDataMap } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/SharedDataMap.sys.mjs"
 );
 const { FileTestUtils } = ChromeUtils.importESModule(
   "resource://testing-common/FileTestUtils.sys.mjs"
diff --git a/toolkit/components/normandy/Normandy.jsm b/toolkit/components/normandy/Normandy.jsm
index ec969a5f4a81..18753660de8d 100644
--- a/toolkit/components/normandy/Normandy.jsm
+++ b/toolkit/components/normandy/Normandy.jsm
@@ -19,6 +19,11 @@ const { setTimeout } = ChromeUtils.importESModule(
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
+  ExperimentManager: "resource://nimbus/lib/ExperimentManager.sys.mjs",
+
+  RemoteSettingsExperimentLoader:
+    "resource://nimbus/lib/RemoteSettingsExperimentLoader.sys.mjs",
+
   TelemetryUtils: "resource://gre/modules/TelemetryUtils.sys.mjs",
 });
 
@@ -33,9 +38,6 @@ XPCOMUtils.defineLazyModuleGetters(lazy, {
   RecipeRunner: "resource://normandy/lib/RecipeRunner.jsm",
   ShieldPreferences: "resource://normandy/lib/ShieldPreferences.jsm",
   TelemetryEvents: "resource://normandy/lib/TelemetryEvents.jsm",
-  ExperimentManager: "resource://nimbus/lib/ExperimentManager.jsm",
-  RemoteSettingsExperimentLoader:
-    "resource://nimbus/lib/RemoteSettingsExperimentLoader.jsm",
 });
 
 var EXPORTED_SYMBOLS = ["Normandy"];
diff --git a/toolkit/components/normandy/actions/MessagingExperimentAction.jsm b/toolkit/components/normandy/actions/MessagingExperimentAction.jsm
index 8606546f017b..c1c66f09c82b 100644
--- a/toolkit/components/normandy/actions/MessagingExperimentAction.jsm
+++ b/toolkit/components/normandy/actions/MessagingExperimentAction.jsm
@@ -10,11 +10,9 @@ const { BaseStudyAction } = ChromeUtils.import(
 
 const lazy = {};
 
-ChromeUtils.defineModuleGetter(
-  lazy,
-  "ExperimentManager",
-  "resource://nimbus/lib/ExperimentManager.jsm"
-);
+ChromeUtils.defineESModuleGetters(lazy, {
+  ExperimentManager: "resource://nimbus/lib/ExperimentManager.sys.mjs",
+});
 
 ChromeUtils.defineModuleGetter(
   lazy,
diff --git a/toolkit/components/normandy/content/AboutPages.jsm b/toolkit/components/normandy/content/AboutPages.jsm
index 6db3dd24615a..2aadd4a9bba5 100644
--- a/toolkit/components/normandy/content/AboutPages.jsm
+++ b/toolkit/components/normandy/content/AboutPages.jsm
@@ -29,16 +29,11 @@ ChromeUtils.defineModuleGetter(
   "RecipeRunner",
   "resource://normandy/lib/RecipeRunner.jsm"
 );
-ChromeUtils.defineModuleGetter(
-  lazy,
-  "ExperimentManager",
-  "resource://nimbus/lib/ExperimentManager.jsm"
-);
-ChromeUtils.defineModuleGetter(
-  lazy,
-  "RemoteSettingsExperimentLoader",
-  "resource://nimbus/lib/RemoteSettingsExperimentLoader.jsm"
-);
+ChromeUtils.defineESModuleGetters(lazy, {
+  ExperimentManager: "resource://nimbus/lib/ExperimentManager.sys.mjs",
+  RemoteSettingsExperimentLoader:
+    "resource://nimbus/lib/RemoteSettingsExperimentLoader.sys.mjs",
+});
 
 var EXPORTED_SYMBOLS = ["AboutPages"];
 
diff --git a/toolkit/components/normandy/lib/LegacyHeartbeat.sys.mjs b/toolkit/components/normandy/lib/LegacyHeartbeat.sys.mjs
index 1df374494c13..501c9f70aff6 100644
--- a/toolkit/components/normandy/lib/LegacyHeartbeat.sys.mjs
+++ b/toolkit/components/normandy/lib/LegacyHeartbeat.sys.mjs
@@ -2,12 +2,10 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
-
 const lazy = {};
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  ExperimentAPI: "resource://nimbus/ExperimentAPI.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
+ChromeUtils.defineESModuleGetters(lazy, {
+  ExperimentAPI: "resource://nimbus/ExperimentAPI.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
 });
 
 const FEATURE_ID = "legacyHeartbeat";
diff --git a/toolkit/components/normandy/test/browser/browser_LegacyHeartbeat.js b/toolkit/components/normandy/test/browser/browser_LegacyHeartbeat.js
index d599031123d8..51713edf7b08 100644
--- a/toolkit/components/normandy/test/browser/browser_LegacyHeartbeat.js
+++ b/toolkit/components/normandy/test/browser/browser_LegacyHeartbeat.js
@@ -13,11 +13,11 @@ const { Heartbeat } = ChromeUtils.import(
   "resource://normandy/lib/Heartbeat.jsm"
 );
 const { Normandy } = ChromeUtils.import("resource://normandy/Normandy.jsm");
-const { ExperimentAPI } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { ExperimentAPI } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 const { RecipeRunner } = ChromeUtils.import(
   "resource://normandy/lib/RecipeRunner.jsm"
diff --git a/toolkit/components/normandy/test/browser/browser_about_studies.js b/toolkit/components/normandy/test/browser/browser_about_studies.js
index 07e193efeba1..3a83d01874b1 100644
--- a/toolkit/components/normandy/test/browser/browser_about_studies.js
+++ b/toolkit/components/normandy/test/browser/browser_about_studies.js
@@ -6,14 +6,14 @@ const { PreferenceExperiments } = ChromeUtils.import(
 const { RecipeRunner } = ChromeUtils.import(
   "resource://normandy/lib/RecipeRunner.jsm"
 );
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
-const { ExperimentManager } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentManager.jsm"
+const { ExperimentManager } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/ExperimentManager.sys.mjs"
 );
-const { RemoteSettingsExperimentLoader } = ChromeUtils.import(
-  "resource://nimbus/lib/RemoteSettingsExperimentLoader.jsm"
+const { RemoteSettingsExperimentLoader } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/RemoteSettingsExperimentLoader.sys.mjs"
 );
 
 const { NormandyTestUtils } = ChromeUtils.import(
diff --git a/toolkit/components/normandy/test/browser/browser_actions_MessagingExperimentAction.js b/toolkit/components/normandy/test/browser/browser_actions_MessagingExperimentAction.js
index 2c86ec5e44de..cb63c9d74130 100644
--- a/toolkit/components/normandy/test/browser/browser_actions_MessagingExperimentAction.js
+++ b/toolkit/components/normandy/test/browser/browser_actions_MessagingExperimentAction.js
@@ -8,8 +8,8 @@ const { MessagingExperimentAction } = ChromeUtils.import(
   "resource://normandy/actions/MessagingExperimentAction.jsm"
 );
 
-const { _ExperimentManager, ExperimentManager } = ChromeUtils.import(
-  "resource://nimbus/lib/ExperimentManager.jsm"
+const { _ExperimentManager, ExperimentManager } = ChromeUtils.importESModule(
+  "resource://nimbus/lib/ExperimentManager.sys.mjs"
 );
 
 decorate_task(
diff --git a/toolkit/components/passwordmgr/LoginManagerParent.jsm b/toolkit/components/passwordmgr/LoginManagerParent.jsm
index cc076bbfdb85..e01a5ca9e52e 100644
--- a/toolkit/components/passwordmgr/LoginManagerParent.jsm
+++ b/toolkit/components/passwordmgr/LoginManagerParent.jsm
@@ -37,12 +37,12 @@ XPCOMUtils.defineLazyGetter(lazy, "PasswordRulesManager", () => {
 ChromeUtils.defineESModuleGetters(lazy, {
   ChromeMigrationUtils: "resource:///modules/ChromeMigrationUtils.sys.mjs",
   MigrationUtils: "resource:///modules/MigrationUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
 });
 
 XPCOMUtils.defineLazyModuleGetters(lazy, {
   FirefoxRelay: "resource://gre/modules/FirefoxRelay.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
   LoginHelper: "resource://gre/modules/LoginHelper.jsm",
   PasswordGenerator: "resource://gre/modules/PasswordGenerator.jsm",
 });
diff --git a/toolkit/components/passwordmgr/test/browser/browser_autocomplete_import.js b/toolkit/components/passwordmgr/test/browser/browser_autocomplete_import.js
index 9dc9e11e48e3..88ebb2e2e7b7 100644
--- a/toolkit/components/passwordmgr/test/browser/browser_autocomplete_import.js
+++ b/toolkit/components/passwordmgr/test/browser/browser_autocomplete_import.js
@@ -1,8 +1,8 @@
 const { ChromeMigrationUtils } = ChromeUtils.import(
   "resource:///modules/ChromeMigrationUtils.jsm"
 );
-const { ExperimentAPI } = ChromeUtils.import(
-  "resource://nimbus/ExperimentAPI.jsm"
+const { ExperimentAPI } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
 );
 
 const { sinon } = ChromeUtils.importESModule(
diff --git a/toolkit/components/pictureinpicture/tests/browser_nimbusFirstTimeStyleVariant.js b/toolkit/components/pictureinpicture/tests/browser_nimbusFirstTimeStyleVariant.js
index e616a3a35bd6..e2b6ff9d9807 100644
--- a/toolkit/components/pictureinpicture/tests/browser_nimbusFirstTimeStyleVariant.js
+++ b/toolkit/components/pictureinpicture/tests/browser_nimbusFirstTimeStyleVariant.js
@@ -3,8 +3,8 @@
 
 "use strict";
 
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 const EXPERIMENT_CLASS_NAME = "experiment";
diff --git a/toolkit/components/pictureinpicture/tests/browser_nimbusMessageFirstTimePip.js b/toolkit/components/pictureinpicture/tests/browser_nimbusMessageFirstTimePip.js
index 03c8edc220e1..7f528299e636 100644
--- a/toolkit/components/pictureinpicture/tests/browser_nimbusMessageFirstTimePip.js
+++ b/toolkit/components/pictureinpicture/tests/browser_nimbusMessageFirstTimePip.js
@@ -3,8 +3,8 @@
 
 "use strict";
 
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 const PIP_EXPERIMENT_MESSAGE = "Hello world message";
diff --git a/toolkit/components/pictureinpicture/tests/browser_nimbusShowIconOnly.js b/toolkit/components/pictureinpicture/tests/browser_nimbusShowIconOnly.js
index 561c151553f4..7217283059c3 100644
--- a/toolkit/components/pictureinpicture/tests/browser_nimbusShowIconOnly.js
+++ b/toolkit/components/pictureinpicture/tests/browser_nimbusShowIconOnly.js
@@ -3,8 +3,8 @@
 
 "use strict";
 
-const { ExperimentFakes } = ChromeUtils.import(
-  "resource://testing-common/NimbusTestUtils.jsm"
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
 );
 
 const PIP_EXPERIMENT_MESSAGE = "Hello world message";
diff --git a/toolkit/components/reader/AboutReader.sys.mjs b/toolkit/components/reader/AboutReader.sys.mjs
index c8e88ed5c605..ea3eac3f4828 100644
--- a/toolkit/components/reader/AboutReader.sys.mjs
+++ b/toolkit/components/reader/AboutReader.sys.mjs
@@ -12,12 +12,8 @@ const lazy = {};
 ChromeUtils.defineESModuleGetters(lazy, {
   AsyncPrefs: "resource://gre/modules/AsyncPrefs.sys.mjs",
   NarrateControls: "resource://gre/modules/narrate/NarrateControls.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
 });
-ChromeUtils.defineModuleGetter(
-  lazy,
-  "NimbusFeatures",
-  "resource://nimbus/ExperimentAPI.jsm"
-);
 
 XPCOMUtils.defineLazyGetter(
   lazy,
diff --git a/toolkit/components/search/SearchEngine.sys.mjs b/toolkit/components/search/SearchEngine.sys.mjs
index 1bf4c1c336f9..f76a57a8b9a3 100644
--- a/toolkit/components/search/SearchEngine.sys.mjs
+++ b/toolkit/components/search/SearchEngine.sys.mjs
@@ -9,13 +9,10 @@ import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   SearchUtils: "resource://gre/modules/SearchUtils.sys.mjs",
 });
 
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-});
-
 const BinaryInputStream = Components.Constructor(
   "@mozilla.org/binaryinputstream;1",
   "nsIBinaryInputStream",
diff --git a/toolkit/components/search/SearchService.sys.mjs b/toolkit/components/search/SearchService.sys.mjs
index d13e07ee8d1b..96aee4cdde2a 100644
--- a/toolkit/components/search/SearchService.sys.mjs
+++ b/toolkit/components/search/SearchService.sys.mjs
@@ -15,6 +15,7 @@ const lazy = {};
 ChromeUtils.defineESModuleGetters(lazy, {
   AddonSearchEngine: "resource://gre/modules/AddonSearchEngine.sys.mjs",
   IgnoreLists: "resource://gre/modules/IgnoreLists.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   OpenSearchEngine: "resource://gre/modules/OpenSearchEngine.sys.mjs",
   PolicySearchEngine: "resource://gre/modules/PolicySearchEngine.sys.mjs",
   Region: "resource://gre/modules/Region.sys.mjs",
@@ -29,7 +30,6 @@ ChromeUtils.defineESModuleGetters(lazy, {
 
 XPCOMUtils.defineLazyModuleGetters(lazy, {
   AddonManager: "resource://gre/modules/AddonManager.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
 });
 
 XPCOMUtils.defineLazyGetter(lazy, "logConsole", () => {
diff --git a/toolkit/components/search/tests/xpcshell/searchconfigs/test_google.js b/toolkit/components/search/tests/xpcshell/searchconfigs/test_google.js
index 42c336dd8e3c..2303efa1148c 100644
--- a/toolkit/components/search/tests/xpcshell/searchconfigs/test_google.js
+++ b/toolkit/components/search/tests/xpcshell/searchconfigs/test_google.js
@@ -3,8 +3,8 @@
 
 "use strict";
 
-XPCOMUtils.defineLazyModuleGetters(this, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
+ChromeUtils.defineESModuleGetters(this, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
 });
 
 const test = new SearchConfigTest({
diff --git a/toolkit/components/search/tests/xpcshell/test_defaultEngine_experiments.js b/toolkit/components/search/tests/xpcshell/test_defaultEngine_experiments.js
index 5fe0ba62b56d..82f4c9368372 100644
--- a/toolkit/components/search/tests/xpcshell/test_defaultEngine_experiments.js
+++ b/toolkit/components/search/tests/xpcshell/test_defaultEngine_experiments.js
@@ -8,8 +8,8 @@
 
 "use strict";
 
-XPCOMUtils.defineLazyModuleGetters(this, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
+ChromeUtils.defineESModuleGetters(this, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
 });
 
 let getVariableStub;
diff --git a/toolkit/components/search/tests/xpcshell/test_telemetry_event_default.js b/toolkit/components/search/tests/xpcshell/test_telemetry_event_default.js
index a5e41d4d889f..2cda61385d9a 100644
--- a/toolkit/components/search/tests/xpcshell/test_telemetry_event_default.js
+++ b/toolkit/components/search/tests/xpcshell/test_telemetry_event_default.js
@@ -10,13 +10,10 @@
 "use strict";
 
 ChromeUtils.defineESModuleGetters(this, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   TelemetryTestUtils: "resource://testing-common/TelemetryTestUtils.sys.mjs",
 });
 
-XPCOMUtils.defineLazyModuleGetters(this, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
-});
-
 const BASE_CONFIG = [
   {
     webExtension: { id: "engine@search.mozilla.org" },
diff --git a/toolkit/components/telemetry/app/TelemetrySend.sys.mjs b/toolkit/components/telemetry/app/TelemetrySend.sys.mjs
index c7722b1500e8..935b5adcd619 100644
--- a/toolkit/components/telemetry/app/TelemetrySend.sys.mjs
+++ b/toolkit/components/telemetry/app/TelemetrySend.sys.mjs
@@ -22,16 +22,12 @@ import { clearTimeout, setTimeout } from "resource://gre/modules/Timer.sys.mjs";
 const lazy = {};
 
 ChromeUtils.defineESModuleGetters(lazy, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   TelemetryHealthPing: "resource://gre/modules/HealthPing.sys.mjs",
   TelemetryReportingPolicy:
     "resource://gre/modules/TelemetryReportingPolicy.sys.mjs",
   TelemetryStorage: "resource://gre/modules/TelemetryStorage.sys.mjs",
 });
-ChromeUtils.defineModuleGetter(
-  lazy,
-  "NimbusFeatures",
-  "resource://nimbus/ExperimentAPI.jsm"
-);
 
 const Utils = TelemetryUtils;
 
diff --git a/toolkit/components/telemetry/dap/DAPTelemetrySender.sys.mjs b/toolkit/components/telemetry/dap/DAPTelemetrySender.sys.mjs
index 0ce983f4a019..f101ae790a56 100644
--- a/toolkit/components/telemetry/dap/DAPTelemetrySender.sys.mjs
+++ b/toolkit/components/telemetry/dap/DAPTelemetrySender.sys.mjs
@@ -12,8 +12,8 @@ XPCOMUtils.defineLazyGetter(lazy, "logConsole", function() {
     maxLogLevelPref: "toolkit.telemetry.dap.logLevel",
   });
 });
-XPCOMUtils.defineLazyModuleGetters(lazy, {
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
+ChromeUtils.defineESModuleGetters(lazy, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
 });
 
 const PREF_LEADER = "toolkit.telemetry.dap_leader";
diff --git a/toolkit/modules/LightweightThemeConsumer.sys.mjs b/toolkit/modules/LightweightThemeConsumer.sys.mjs
index 317eb0770fd7..b48d07c65865 100644
--- a/toolkit/modules/LightweightThemeConsumer.sys.mjs
+++ b/toolkit/modules/LightweightThemeConsumer.sys.mjs
@@ -10,17 +10,12 @@ const lazy = {};
 // Get the theme variables from the app resource directory.
 // This allows per-app variables.
 ChromeUtils.defineESModuleGetters(lazy, {
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
   ThemeContentPropertyList: "resource:///modules/ThemeVariableMap.sys.mjs",
   ThemeVariableMap: "resource:///modules/ThemeVariableMap.sys.mjs",
 });
 
-ChromeUtils.defineModuleGetter(
-  lazy,
-  "NimbusFeatures",
-  "resource://nimbus/ExperimentAPI.jsm"
-);
-
 // Whether the content and chrome areas should always use the same color
 // scheme (unless user-overridden). Thunderbird uses this.
 XPCOMUtils.defineLazyPreferenceGetter(
diff --git a/toolkit/modules/Troubleshoot.sys.mjs b/toolkit/modules/Troubleshoot.sys.mjs
index 57d613146f1d..0e5ee7eb44c2 100644
--- a/toolkit/modules/Troubleshoot.sys.mjs
+++ b/toolkit/modules/Troubleshoot.sys.mjs
@@ -973,8 +973,8 @@ var dataProviders = {
     const {
       PreferenceRollouts: NormandyPreferenceRollouts,
     } = ChromeUtils.import("resource://normandy/lib/PreferenceRollouts.jsm");
-    const { ExperimentManager } = ChromeUtils.import(
-      "resource://nimbus/lib/ExperimentManager.jsm"
+    const { ExperimentManager } = ChromeUtils.importESModule(
+      "resource://nimbus/lib/ExperimentManager.sys.mjs"
     );
 
     // Get Normandy data in parallel, and sort each group by slug.
diff --git a/toolkit/mozapps/extensions/content/aboutaddons.js b/toolkit/mozapps/extensions/content/aboutaddons.js
index 306f062b1f7b..4c4bf17714a8 100644
--- a/toolkit/mozapps/extensions/content/aboutaddons.js
+++ b/toolkit/mozapps/extensions/content/aboutaddons.js
@@ -14,6 +14,7 @@ ChromeUtils.defineESModuleGetters(this, {
   ClientID: "resource://gre/modules/ClientID.sys.mjs",
   DeferredTask: "resource://gre/modules/DeferredTask.sys.mjs",
   E10SUtils: "resource://gre/modules/E10SUtils.sys.mjs",
+  NimbusFeatures: "resource://nimbus/ExperimentAPI.sys.mjs",
   PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
 });
 
@@ -24,7 +25,6 @@ XPCOMUtils.defineLazyModuleGetters(this, {
   ExtensionCommon: "resource://gre/modules/ExtensionCommon.jsm",
   ExtensionParent: "resource://gre/modules/ExtensionParent.jsm",
   ExtensionPermissions: "resource://gre/modules/ExtensionPermissions.jsm",
-  NimbusFeatures: "resource://nimbus/ExperimentAPI.jsm",
 });
 
 XPCOMUtils.defineLazyGetter(this, "browserBundle", () => {