Ubuntu 10.04 LTS is shipped with Mozilla Firefox 3.6 by default. In order to upgrade it to Firefox 8 to support HTML5 and CSS3, we will have to add Mozilla Firefox repository.
First, open up your terminal and enter the following:
gksu add-apt-repository ppa:mozillateam/firefox-stable
Next, update the repositories:
sudo apt-get update
Lastly, install Firefox 8:
sudo apt-get install firefox