--- a/modules/libpref/Preferences.cpp
+++ b/modules/libpref/Preferences.cpp
@@ -3271,17 +3271,17 @@ public:
   PrefChangedFunc mCallback;
   Preferences::MatchKind mMatchKind;
 };
 
 class ValueObserver final
   : public nsIObserver
   , public ValueObserverHashKey
 {
-  ~ValueObserver() { Preferences::RemoveObserver(this, mPrefName.get()); }
+  ~ValueObserver() = default;
 
 public:
   NS_DECL_ISUPPORTS
   NS_DECL_NSIOBSERVER
 
   ValueObserver(const char* aPref,
                 PrefChangedFunc aCallback,
                 Preferences::MatchKind aMatchKind)
@@ -5064,19 +5064,20 @@ Preferences::RegisterCallback(PrefChange
   gObserverTable->Get(&hashKey, getter_AddRefs(observer));
   if (observer) {
     observer->AppendClosure(aClosure);
     return NS_OK;
   }
 
   observer = new ValueObserver(aPref, aCallback, aMatchKind);
   observer->AppendClosure(aClosure);
-  nsresult rv = AddStrongObserver(observer, aPref);
-  NS_ENSURE_SUCCESS(rv, rv);
-
+  PREF_RegisterCallback(aPref,
+                        NotifyObserver,
+                        static_cast<nsIObserver*>(observer),
+                        /* isPriority */ false);
   gObserverTable->Put(observer, observer);
   return NS_OK;
 }
 
 /* static */ nsresult
 Preferences::RegisterCallbackAndCall(PrefChangedFunc aCallback,
                                      const char* aPref,
                                      void* aClosure,
@@ -5108,16 +5109,19 @@ Preferences::UnregisterCallback(PrefChan
   gObserverTable->Get(&hashKey, getter_AddRefs(observer));
   if (!observer) {
     return NS_OK;
   }
 
   observer->RemoveClosure(aClosure);
   if (observer->HasNoClosures()) {
     // Delete the callback since its list of closures is empty.
+    MOZ_ALWAYS_SUCCEEDS(
+      PREF_UnregisterCallback(aPref, NotifyObserver, observer));
+
     gObserverTable->Remove(observer);
   }
   return NS_OK;
 }
 
 // We insert cache observers using RegisterPriorityCallback to ensure they are
 // called prior to ordinary pref observers. Doing this ensures that ordinary
 // observers will never get stale values from cache variables.