Firefox 3.5 just came out today and it claims to have doubled performance over Firefox 3.0. I'm using it right now, and the page loads seem noticeably snappier.

Here's a snippet from the Press Release:

"Firefox 3.5 is the best performing browser Mozilla has ever released and delivers radically improved JavaScript performance, a new Private Browsing mode, native support for open video and audio, and Location Aware Browsing. The newest version of Firefox is more than two times faster than Firefox 3 and ten times faster than Firefox 2 on complex websites. With extensive under-the-hood work to support new technologies, Firefox 3.5 is the most powerful and complete modern browser and helps upgrade the Web experience."

You can download it here:

http://www.mozilla.com/en-US/