I ran Firefox beta off and on, and it was fine but a bit buggy.  Then I download FF4 final release and it was REALLY buggy.  Screens not fully rendering, browser getting stuck, buttons not working, etc..  Never did fully crash though funny enough.Even killing the browser and restarting did not help.

I then started to take off plugins and ‘boom’ firefox is living up to the hype.  I’m not sure which of the plugin was killing it, Although I have a feeling it was Mcafee.  But could have been the website speed extensions as well.  I do not need them and have not bothered turning them on one by one to find out.

So, all excited with Firefox and the things keep locking up on you? Even when you close and reopen the browser?  Start killing extentions.

Good luck!