I can't help you, but I've had some trouble with Firefox, too.  I wiped the hard drive on my Mac--for other reasons--and I didn't reinstall Firefox because they darn thing was getting glitchy and running slowly.
Not only that, but on two separate PCs I occasionally use, Firefox won't run at all for some reason.  I installed the update and it just won't connect to the net with Firefox.
So, something's screwy.  Sorry I can't actually offer any advice.