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.