Just installed an unnecessary amount of Firefoxes, via Gregory Koberger:

curl -L -O https://github.com/omgmog/install-all-firefox/raw/master/install-all-firefox.sh
chmod +x install-all-firefox.sh
./install-all-firefox.sh [version] [locale]

Version and locale are option. If you don’t use a locale, it will try to figure out your locale. If you don’t have a version, it will install all available versions of Firefox.

If you want to see what’s available (and what you have installed):

./install-all-firefox.sh status

The benefit of installing this way is that now Add-Ons are profiled; so the latest release of Firebug won’t complain when I launch an older, incompatible version of Firefox.