A quick update for Ubuntu 10.10 / 10.04 users: Firefox 5 has just been uploaded to the Firefox Stable PPA. Ubuntu 11.04 users do not have to add any PPA because Firefox 5 is available in the official Ubuntu 11.04 repositories so all you have to do is run a regular update.
You can install Firefox 5 in Ubuntu 10.10 or 10.04 using the commands below:
sudo add-apt-repository ppa:mozillateam/firefox-stable
sudo apt-get update
sudo apt-get upgrade
