My only suggestion is a full uninstall/install. Perhaps you've already tried that?
I've been having my own problems with Firefox 2 recently. It sometimes locks solid for no apparent reason. The only way over it is to shut it down with the old 3-finger salute. I never updated to Firefox 3 as I've seen reports that it's buggy & doesn't support some of my favourite plugins.
I assume it was the plugin's. I have just managed to get it to start. I downloaded 3.0 again and then managed to start it in safe mode at last. I disabled the plugins and all now seems to be fine. I would prefer 2.X due to a couple of plugins, but now it is running I will leave well a loan.
Matt