I'm running Firefox on Vista with no problem. It has these weird periods of slowness/not responding shortly after booting, but that could be AVG tying up CPU time while scanning for viruses.
That's most likely an issue with the firewall. At least that seems to be the usual cause for that problem on Vista so far.
Through the intercession of Our Lady of Mount Carmel, may Jesus Christ bless you abundantly.
Pray that we may be one, as Christ and His Father are one. (John 17:20ff)
A.K.A. - JMJ_coder