diff --git a/browser/components/preferences/main.js b/browser/components/preferences/main.js
index 363f7f7978f1..2f7d5d7c8922 100644
--- a/browser/components/preferences/main.js
+++ b/browser/components/preferences/main.js
@@ -1877,6 +1877,18 @@ var gMainPane = {
       return;
     }
 
+    // Track how often locale fallback order is changed.
+    // Drop the first locale and filter to only include the overlapping set
+    const prevLocales = Services.locale.requestedLocales.filter(
+      lc => selected.indexOf(lc) > 0
+    );
+    const newLocales = selected.filter(
+      (lc, i) => i > 0 && prevLocales.includes(lc)
+    );
+    if (prevLocales.some((lc, i) => newLocales[i] != lc)) {
+      this.gBrowserLanguagesDialog.recordTelemetry("set_fallback");
+    }
+
     switch (gMainPane.getLanguageSwitchTransitionType(selected)) {
       case "requires-restart":
         gMainPane.showConfirmLanguageChangeMessageBar(selected);
diff --git a/browser/components/preferences/tests/browser_browser_languages_subdialog.js b/browser/components/preferences/tests/browser_browser_languages_subdialog.js
index d089f0867024..96754332671d 100644
--- a/browser/components/preferences/tests/browser_browser_languages_subdialog.js
+++ b/browser/components/preferences/tests/browser_browser_languages_subdialog.js
@@ -441,6 +441,24 @@ add_task(async function testReorderingBrowserLanguages() {
     "The second dialog id is larger than the first"
   );
 
+  // Open the dialog yet again.
+  newDialog = await openDialog(doc);
+  dialog = newDialog.dialog;
+  dialogDoc = newDialog.dialogDoc;
+  let thirdDialogId = getDialogId(dialogDoc);
+  selected = newDialog.selected;
+
+  // Move pl to the top.
+  selectAddedLocale("pl", selected);
+  assertLocaleOrder(selected, "en-US,he,pl", "pl");
+  dialogDoc.getElementById("up").doCommand();
+  dialogDoc.getElementById("up").doCommand();
+  assertLocaleOrder(selected, "pl,en-US,he", "pl");
+
+  dialogClosed = BrowserTestUtils.waitForEvent(dialog, "dialogclosing");
+  dialog.acceptDialog();
+  await dialogClosed;
+
   await Promise.all(addons.map(addon => addon.uninstall()));
   BrowserTestUtils.removeTab(gBrowser.selectedTab);
 
@@ -448,9 +466,14 @@ add_task(async function testReorderingBrowserLanguages() {
     ["manage", "main", firstDialogId],
     ["reorder", "dialog", firstDialogId],
     ["accept", "dialog", firstDialogId],
+    ["set_fallback", "dialog", firstDialogId],
     ["manage", "main", secondDialogId],
     ["reorder", "dialog", secondDialogId],
     ["accept", "dialog", secondDialogId],
+    ["manage", "main", thirdDialogId],
+    ["reorder", "dialog", thirdDialogId],
+    ["reorder", "dialog", thirdDialogId],
+    ["accept", "dialog", thirdDialogId],
   ]);
 });
 
diff --git a/toolkit/components/telemetry/Events.yaml b/toolkit/components/telemetry/Events.yaml
index 2359b25e84c1..f6db78b14995 100644
--- a/toolkit/components/telemetry/Events.yaml
+++ b/toolkit/components/telemetry/Events.yaml
@@ -2601,6 +2601,7 @@ intl.ui.browserLanguage:
       - apply
       - accept
       - cancel
+      - set_fallback
     extra_keys:
       installId: The id for an install.
     products:
@@ -2609,6 +2610,7 @@ intl.ui.browserLanguage:
     notification_emails:
       - flod@mozilla.com
       - mstriemer@mozilla.com
+      - earo@mozilla.com
     release_channel_collection: opt-out
     record_in_processes: ["main"]
     bug_numbers:
@@ -2619,6 +2621,7 @@ intl.ui.browserLanguage:
       - 1739288
       - 1796396
       - 1861299
+      - 1911321
 
 network.dns:
   trrConfirmation: