I am running Firefox 3.05 right now, though it is up to 3.06, just haven't updated. I have not had problems with it. One thing to try when you do download is begin without the add-ons, then add them one at a time. This way you'll see what might be causing the trouble.
Be sure that cookie settings are correct...only 1st party cookies in IE, NO 3rd party cookies and in Firefox only accept cookies has a check mark and 3rd party has none.