Backing out dea6175f4b07 (bug 584864) to fix regression filed as bug 585606

content/base/src/nsFrameLoader.cpp

@@ -1889,10 +1889,6 @@ nsFrameLoader::EnsureMessageManager()
     return rv;
   }
 
-  if (!mIsTopLevelContent) {
-    return NS_OK;
-  }
-
   if (mMessageManager) {
 #ifdef MOZ_IPC
     if (ShouldUseRemoteProcess()) {