I have had a few people ask recently how to run multiple versions of Firefox on the one Windows machine. The procedure is the same for Linux.
What you need to do is to install each version of Firefox into it’s own folder with a different profile for execution.
On Windows, create shortcuts like this:
“C:\Program files\Firefox\Firefox-1.5\firefox.exe” -p Firefox-1.5 -no-remote
“C:\Program files\Firefox\Firefox-2.0\firefox.exe” -p Firefox-2.0 -no-remote
“C:\Program files\Firefox\Firefox-3.0\firefox.exe” -p Firefox-3.0 -no-remote
Away you go…