Which version of firefox you using? the lastest ive got is 2.0.0.2 and i dont have any problems at all, infact ive never had that problem and ive been using FF for over a year!
You could try resetting the toolbars, click on startbar then programmes and find FF folder, then go to "safemode", providing you havent got FF running you will get a box pop up, check the box that says reset toolbars, and see if that does anything