I beleive your software has been compromized - I was hacked after downloading firefox optimized for yahoo. Does that even exist? if so it has been hacked.
Yesterday I downloaded a 'firefox optimized for yahoo' app. Then last night my yahoo email was hacked and all emails and contacts deleted. I believe the app I downloaded may have been false? or your yahoo optimization was hacked.
Where did you get that "app" from?
Or did you purposely install the Yahoo optimized version of Firefox 5.0, which is almost 2 years old? And not made by Mozilla!
The best place to get Firefox is from Mozilla directly, not from a 3rd party website which may have done "who knows what" as far as "tweaks".