Best Firefox version?

[XabbaRus]

I reinstalled Windows XP last night and was wondering what was the best build of Firefox, or should I use Windows 8

The reason I am asking is with the later versions of Firefox I would get something quite intriguing. When I was visiting some sites, usually with a Flash animation or maybe not, eg f1sportnetwork site my fan would suddenly kick into high speed and the CPU load would jump up to 80%, all for a bloody web page.

Now I thought I might have a virus but came up with nothing. I would also notice tha FF memory usage would have shot right up too....I'd shut down FF and things would go back to normal, so any suggestions?

At the moment I am using IE8