Steve,
I had a shitload of problems with firefox 3 also.
It had to do with the skype plugin for firefox.
I was getting performance issues, and it plain would not load certain images.
I disabled the plugin, it seems to be running OK for now.
Honestly, I started fucking around with opera 9, that seems to be faster.
My system isn’t state of the art at all (P4, 2gb, SATA drives, PCIX Card), but it should render web pages a bit faster.
I might just put ubuntu on it and see what that does.