running firefox 4 and firefox 3 side by side on ubuntu

Firefox 4 just dropped and you want to try it without losing your current setup? You can run both versions at the same time.

Add the Mozilla Daily PPA, update, then install:

sudo add-apt-repository ppa:ubuntu-mozilla-daily/ppa
sudo apt-get update
sudo apt-get install firefox-4.0

Firefox 3 stays as firefox. Firefox 4 runs as firefox-4.0. Both show up in your applications menu, or you can launch them from the terminal whichever you need.