--- a/intl/locale/LocaleService.cpp
+++ b/intl/locale/LocaleService.cpp
@@ -177,28 +177,28 @@ LocaleService*
 LocaleService::GetInstance()
 {
   if (!sInstance) {
     sInstance = new LocaleService(XRE_IsParentProcess());
 
     if (sInstance->IsServer()) {
       // We're going to observe for requested languages changes which come
       // from prefs.
-      DebugOnly<nsresult> rv = Preferences::AddStrongObservers(sInstance, kObservedPrefs);
+      DebugOnly<nsresult> rv = Preferences::AddWeakObservers(sInstance, kObservedPrefs);
       MOZ_ASSERT(NS_SUCCEEDED(rv), "Adding observers failed.");
     }
     ClearOnShutdown(&sInstance);
   }
   return sInstance;
 }
 
 LocaleService::~LocaleService()
 {
   if (mIsServer) {
-    Preferences::RemoveObservers(sInstance, kObservedPrefs);
+    Preferences::RemoveObservers(this, kObservedPrefs);
   }
 }
 
 void
 LocaleService::GetAppLocalesAsLangTags(nsTArray<nsCString>& aRetVal)
 {
   if (mAppLocales.IsEmpty()) {
     NegotiateAppLocales(mAppLocales);

--- a/intl/locale/LocaleService.h
+++ b/intl/locale/LocaleService.h
@@ -4,16 +4,17 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #ifndef mozilla_intl_LocaleService_h__
 #define mozilla_intl_LocaleService_h__
 
 #include "nsIObserver.h"
 #include "nsString.h"
 #include "nsTArray.h"
+#include "nsWeakReference.h"
 
 #include "mozILocaleService.h"
 
 namespace mozilla {
 namespace intl {
 
 /**
  * LocaleService is a manager of language negotiation in Gecko.
@@ -63,17 +64,18 @@ namespace intl {
  *
  * An example of a Locale ID is `en-Latn-US-x-hc-h12-ca-gregory`
  *
  * At the moment we do not support full extension tag system, but we
  * try to be specific when naming APIs, so the service is for locales,
  * but we negotiate between languages etc.
  */
 class LocaleService : public mozILocaleService,
-                      public nsIObserver
+                      public nsIObserver,
+                      public nsSupportsWeakReference
 {
 public:
   NS_DECL_ISUPPORTS
   NS_DECL_NSIOBSERVER
   NS_DECL_MOZILOCALESERVICE
 
   /**
    * List of available language negotiation strategies.