Open a Terminal from Applications > Accessories
And execute the following commands,
You can see Firefox 4 appeared in Applications > Internet > Minefield 4.0
And execute the following commands,
sudo add-apt-repository ppa:ubuntu-mozilla-daily/ppa
sudo apt-get update
sudo apt-get install firefox-4.0
sudo apt-get update
sudo apt-get install firefox-4.0
You can see Firefox 4 appeared in Applications > Internet > Minefield 4.0
