LOL, thats kinda of funny. You might have downloaded a <XXXXXX> fake firefox? or someones just screwing with you! thatts kind of funny!
and it could be one of your toolbars you have up there doing it. unlock the toolbars and tale all of them off. right click and see if its there. If it isn't, enable them 1 by 1 to see which one it is. Tell us if its one, which one!
EDIT; post was reported for bad language