--- a/uriloader/prefetch/nsOfflineCacheUpdateService.cpp
+++ b/uriloader/prefetch/nsOfflineCacheUpdateService.cpp
@@ -252,16 +252,19 @@ nsOfflineCacheUpdateService::nsOfflineCa
     Preferences::AddBoolVarCache(&sAllowOfflineCache,
                                  "browser.cache.offline.enable",
                                  true);
 }
 
 nsOfflineCacheUpdateService::~nsOfflineCacheUpdateService()
 {
     gOfflineCacheUpdateService = nullptr;
+
+    delete mAllowedDomains;
+    mAllowedDomains = nullptr;
 }
 
 nsresult
 nsOfflineCacheUpdateService::Init()
 {
     // Observe xpcom-shutdown event
     nsCOMPtr<nsIObserverService> observerService =
       mozilla::services::GetObserverService();