I'll guide you throough it.
1) Download firefox-1.0.tar.gz from
mozilla's ftp site. Save it somewhere in your /home directory.
2) Start a console/terminal session and switch to root
3) Change directory to /usr/local
4) Untar firefox e.g. #tar -zxvf /home/userid/downloads/firefox-1.0.tar.gz
5) make a symlink to firefox, e.g. #ln -s /usr/local/firefox/firefox /usr/bin/firefox
Once thats done, exit as root and type "firefox" at the console, it should start.