Created attachment 712686 [details] Screenshot It's difficult to describe, I'm attaching a screenshot. I can reproduce this problem if I disable Facebook Messenger, then close and re-open Firefox.
This sounds like a problem fix in bug 837027 - but that patch landed on m-c on 2013-02-06. Can you please confirm the problem doesn't exist in nightlies since that date? If so, this can be marked as a dupe of that bug (which will also be landing in a simplified form on Aurora)
Yeah, looks fixed in a recent build.