As noted at tuxradar.com, the new firefox 3.5 beta for has significant speed improvements for running native on linux. Bloggers have complained that the current version is unnecessarily slow, and even that they prefer running the windows version in wine. To compare the speed changes for yourself, or just to take a look at how it is progressing, install it like this:
tar xvfj firefox-3.5b4.tar.bz2
chmod +x firefox/firefox
ln firefox/firefox Firefox
mv Firefox Desktop/
This also creates an icon on the desktop. To run, simply double click this icon.