Install FireFox3.5 in Ubuntu

1. Download latest version firefox from mozilla.org and save the file to your path Public
   
2. Open a terminal and cd Public dir
   
3. tar xfvj firefox-3.5rc2.tar.bz2
4. sudo mv firefox /usr/lib/
5. cd /usr/lib/
6. ln -s /usr/lib/firefox/firefox /usr/bin/firefox

if /usr/bin/firefox link to the old version just remove that, and this update failed you could point to the old firefox again.

good luck,