See this page for a way to install multiple Firefox versions *http://www.businessinsider.com/how-to-run-firefox-4-and-3-simultaneously-in-mac-os-x-with-multiple-firefox-profiles-2011-3 * https://ftp.mozilla.org/pub/mozilla.org/firefox/releases/2.0.0.20/mac/en-US/ ---- You can also look at a portable version: *http://sourceforge.net/projects/osxportableapps/files/Portable%20Firefox%20OS%20X/ *http://www.freesmug.org/portableapps/firefox/