Here Mozilla releases you can download firefox 3.6. The setup is in your language folder. Before you install this version i must tell you that is dangerous to install a old version of firefox for your security when you surf the net.

See this article about how to install multiple versions on Mac OS X:

• http://www.businessinsider.com/how-to-run-firefox-4-and-3-simultaneously-in-mac-os-x-with-multiple-firefox-profiles-2011-3

I current run 24, I don't have 3.6. I need 3.6

Sorry this is the correct link to download firefox 3.6 for mac http://ftp://ftp.mozilla.org/pub/firefox/releases/3.6/mac/