Install Firefox 4 in Ubuntu 10.04 / 10.10 | Here’s how to upgrade your Firefox 3.x in Ubuntu to Firefox 4 using the Mozilla stable ppa. Simply issue these commands one after another: $ sudo add-apt-repository ppa:mozillateam/firefox-stable $ sudo apt-get update $ sudo apt-get install firefox ubufox Your existing Firefox will be replaced with the new Firefox 4.