--- a/dom/events/EventDispatcher.cpp
+++ b/dom/events/EventDispatcher.cpp
@@ -675,16 +675,18 @@ EventDispatcher::Dispatch(nsISupports* a
   // sure it is initialized!
   // If aTargets is non-null, the event isn't going to be dispatched.
   NS_ENSURE_TRUE(aEvent->mMessage || !aDOMEvent || aTargets,
                  NS_ERROR_DOM_INVALID_STATE_ERR);
 
   // Events shall not be fired while we are in stable state to prevent anything
   // visible from the scripts.
   MOZ_ASSERT(!nsContentUtils::IsInStableOrMetaStableState());
+  NS_ENSURE_TRUE(!nsContentUtils::IsInStableOrMetaStableState(),
+                 NS_ERROR_DOM_INVALID_STATE_ERR);
 
 #ifdef MOZ_TASK_TRACER
   if (MOZ_UNLIKELY(mozilla::tasktracer::IsStartLogging())) {
     nsAutoCString eventType;
     nsAutoString eventTypeU16;
     if (aDOMEvent) {
       aDOMEvent->GetType(eventTypeU16);
     } else {