How to keep your Firefox installation simple:
This works for me, and the 20+ exployees that use my workstations daily. It should work for you.
1 - Download Firefox from mozilla:
http://www.mozilla.org/products/firefox/all.html
2 - Become superuser
3 - Untar it (or unzip it) to a folder
4 - Run the install script from that folder
5 - Install it to /firefox
(That's right. No directories. No subdirectories. Just plain / )
6 - cd to your /firefox directory
7 - chmod 777 -R *
8 - Enjoy Firefox with any user! Simply have an icon on their desktop that points to:
/firefox/firefox
Cheers