I would suggest using Chrome or IE9, if you have Windows 7 or Vista (who would have Vista
). IE9 is awesome. My only beef with IE9 is the placement of the URL box.
I have FF 4 on my work PC and find it's not compatible with some of our intranet sites and often have to downgrade our users back to 3.6. FF 4 isn't very good, I don't have it installed on my home PC to test though. FF 3.6 loads T4R.org website just fine.
IMO, FF is not what it use to be and has definitely lost its luster with me. I will not be reinstalling FF on any Windows 7 rigs of mine, IE9 and Chrome only.