diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
index c6226471c7ea..04ef3e21176c 100644
--- a/modules/libpref/init/StaticPrefList.yaml
+++ b/modules/libpref/init/StaticPrefList.yaml
@@ -14062,6 +14062,12 @@
   value: 1048576
   mirror: always
 
+# If true, use the HSTS preload list.
+- name: network.stricttransportsecurity.preloadlist
+  type: RelaxedAtomicBool
+  value: true
+  mirror: always
+
 # DNS Trusted Recursive Resolver
 # 0 - default off, 1 - reserved/off, 2 - TRR first, 3 - TRR only,
 # 4 - reserved/off, 5 off by choice
@@ -17018,6 +17024,13 @@
 # Prefs starting with "test."
 #---------------------------------------------------------------------------
 
+# A mechanism to make the current time seem later than it is for specific
+# operations. Currently used to test expiration of the HSTS preload list.
+- name: test.currentTimeOffsetSeconds
+  type: RelaxedAtomicUint32
+  value: 0
+  mirror: always
+
 - name: test.events.async.enabled
   type: RelaxedAtomicBool
   value: false
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index 503a3e9744ca..db49b40a3203 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -1474,9 +1474,6 @@ pref("network.proxy.autoconfig_retry_interval_min", 5);    // 5 seconds
 pref("network.proxy.autoconfig_retry_interval_max", 300);  // 5 minutes
 pref("network.proxy.enable_wpad_over_dhcp", true);
 
-// Use the HSTS preload list by default
-pref("network.stricttransportsecurity.preloadlist", true);
-
 pref("converter.html2txt.structs",          true); // Output structured phrases (strong, em, code, sub, sup, b, i, u)
 pref("converter.html2txt.header_strategy",  1); // 0 = no indention; 1 = indention, increased with header level; 2 = numbering and slight indention
 
diff --git a/security/manager/ssl/nsSiteSecurityService.cpp b/security/manager/ssl/nsSiteSecurityService.cpp
index da2563028269..7fb4bf0e9883 100644
--- a/security/manager/ssl/nsSiteSecurityService.cpp
+++ b/security/manager/ssl/nsSiteSecurityService.cpp
@@ -9,7 +9,8 @@
 #include "mozilla/Base64.h"
 #include "mozilla/LinkedList.h"
 #include "mozilla/Logging.h"
-#include "mozilla/Preferences.h"
+#include "mozilla/StaticPrefs_network.h"
+#include "mozilla/StaticPrefs_test.h"
 #include "mozilla/Tokenizer.h"
 #include "mozilla/dom/PContent.h"
 #include "mozilla/dom/ToJSValue.h"
@@ -22,7 +23,6 @@
 #include "nsPromiseFlatString.h"
 #include "nsReadableUtils.h"
 #include "nsSecurityHeaderParser.h"
-#include "nsThreadUtils.h"
 #include "nsVariant.h"
 #include "nsXULAppAPI.h"
 #include "prnetdb.h"
@@ -167,28 +167,13 @@ void SiteHSTSState::ToString(nsCString& aString) {
   aString.AppendInt(static_cast<uint32_t>(mHSTSIncludeSubdomains));
 }
 
-nsSiteSecurityService::nsSiteSecurityService()
-    : mUsePreloadList(true), mPreloadListTimeOffset(0), mDafsa(kDafsa) {}
+nsSiteSecurityService::nsSiteSecurityService() : mDafsa(kDafsa) {}
 
 nsSiteSecurityService::~nsSiteSecurityService() = default;
 
-NS_IMPL_ISUPPORTS(nsSiteSecurityService, nsIObserver, nsISiteSecurityService)
+NS_IMPL_ISUPPORTS(nsSiteSecurityService, nsISiteSecurityService)
 
 nsresult nsSiteSecurityService::Init() {
-  // Don't access Preferences off the main thread.
-  if (!NS_IsMainThread()) {
-    MOZ_ASSERT_UNREACHABLE("nsSiteSecurityService initialized off main thread");
-    return NS_ERROR_NOT_SAME_THREAD;
-  }
-
-  mUsePreloadList = mozilla::Preferences::GetBool(
-      "network.stricttransportsecurity.preloadlist", true);
-  mozilla::Preferences::AddStrongObserver(
-      this, "network.stricttransportsecurity.preloadlist");
-  mPreloadListTimeOffset =
-      mozilla::Preferences::GetInt("test.currentTimeOffsetSeconds", 0);
-  mozilla::Preferences::AddStrongObserver(this,
-                                          "test.currentTimeOffsetSeconds");
   nsCOMPtr<nsIDataStorageManager> dataStorageManager(
       do_GetService("@mozilla.org/security/datastoragemanager;1"));
   if (!dataStorageManager) {
@@ -764,8 +749,11 @@ bool nsSiteSecurityService::GetPreloadStatus(const nsACString& aHost,
   const int kIncludeSubdomains = 1;
   bool found = false;
 
-  PRTime currentTime = PR_Now() + (mPreloadListTimeOffset * PR_USEC_PER_SEC);
-  if (mUsePreloadList && currentTime < gPreloadListExpirationTime) {
+  PRTime currentTime =
+      PR_Now() +
+      (StaticPrefs::test_currentTimeOffsetSeconds() * (PRTime)PR_USEC_PER_SEC);
+  if (StaticPrefs::network_stricttransportsecurity_preloadlist() &&
+      currentTime < gPreloadListExpirationTime) {
     int result = mDafsa.Lookup(aHost);
     found = (result != mozilla::Dafsa::kKeyNotFound);
     if (found && aIncludeSubdomains) {
@@ -991,26 +979,3 @@ nsresult nsSiteSecurityService::IsSecureHost(
 
 NS_IMETHODIMP
 nsSiteSecurityService::ClearAll() { return mSiteStateStorage->Clear(); }
-
-//------------------------------------------------------------
-// nsSiteSecurityService::nsIObserver
-//------------------------------------------------------------
-
-NS_IMETHODIMP
-nsSiteSecurityService::Observe(nsISupports* /*subject*/, const char* topic,
-                               const char16_t* /*data*/) {
-  // Don't access Preferences off the main thread.
-  if (!NS_IsMainThread()) {
-    MOZ_ASSERT_UNREACHABLE("Preferences accessed off main thread");
-    return NS_ERROR_NOT_SAME_THREAD;
-  }
-
-  if (strcmp(topic, NS_PREFBRANCH_PREFCHANGE_TOPIC_ID) == 0) {
-    mUsePreloadList = mozilla::Preferences::GetBool(
-        "network.stricttransportsecurity.preloadlist", true);
-    mPreloadListTimeOffset =
-        mozilla::Preferences::GetInt("test.currentTimeOffsetSeconds", 0);
-  }
-
-  return NS_OK;
-}
diff --git a/security/manager/ssl/nsSiteSecurityService.h b/security/manager/ssl/nsSiteSecurityService.h
index f5de35936a49..a11a2d120123 100644
--- a/security/manager/ssl/nsSiteSecurityService.h
+++ b/security/manager/ssl/nsSiteSecurityService.h
@@ -10,7 +10,6 @@
 #include "mozilla/RefPtr.h"
 #include "nsCOMPtr.h"
 #include "nsIDataStorage.h"
-#include "nsIObserver.h"
 #include "nsISiteSecurityService.h"
 #include "nsString.h"
 #include "nsTArray.h"
@@ -22,12 +21,8 @@ class nsIURI;
 using mozilla::OriginAttributes;
 
 // {16955eee-6c48-4152-9309-c42a465138a1}
-#define NS_SITE_SECURITY_SERVICE_CID                 \
-  {                                                  \
-    0x16955eee, 0x6c48, 0x4152, {                    \
-      0x93, 0x09, 0xc4, 0x2a, 0x46, 0x51, 0x38, 0xa1 \
-    }                                                \
-  }
+#define NS_SITE_SECURITY_SERVICE_CID \
+  {0x16955eee, 0x6c48, 0x4152, {0x93, 0x09, 0xc4, 0x2a, 0x46, 0x51, 0x38, 0xa1}}
 
 /**
  * SecurityPropertyState: A utility enum for representing the different states
@@ -90,11 +85,9 @@ class SiteHSTSState {
 
 struct nsSTSPreload;
 
-class nsSiteSecurityService : public nsISiteSecurityService,
-                              public nsIObserver {
+class nsSiteSecurityService : public nsISiteSecurityService {
  public:
   NS_DECL_THREADSAFE_ISUPPORTS
-  NS_DECL_NSIOBSERVER
   NS_DECL_NSISITESECURITYSERVICE
 
   nsSiteSecurityService();
@@ -149,8 +142,6 @@ class nsSiteSecurityService : public nsISiteSecurityService,
                                const OriginAttributes& aOriginAttributes,
                                nsIDataStorage::DataType aDataStorageType);
 
-  bool mUsePreloadList;
-  int64_t mPreloadListTimeOffset;
   nsCOMPtr<nsIDataStorage> mSiteStateStorage;
   const mozilla::Dafsa mDafsa;
 };