Bug 1585582 - Don't parse manifest when storage is disabled r=baku

Differential Revision: https://phabricator.services.mozilla.com/D47958

--HG--
extra : moz-landing-system : lando

dom/base/nsContentSink.cpp

@@ -998,6 +998,11 @@ void nsContentSink::ProcessOfflineManifest(const nsAString& aManifestSpec) {
     return;
   }
 
+  // If offline storage is disabled skip processing
+  if (!StaticPrefs::browser_cache_offline_storage_enable()) {
+    return;
+  }
+
   // If this document has been interecepted, let's skip the processing of the
   // manifest.
   if (mDocument->GetController().isSome()) {