Only the Official builds of Firefox from www.mozilla.org/firefox/all get internal updates from Mozilla. Third-party builds that you built yourself or by a third-party such as a Linux distro provided package do not get updates from Mozilla as how can they provide updates for builds they did not well build. You will either have to get update from Ubuntu If they still even provide package updates to this old 10.04 LTS from April 2011. Or you get Firefox from www.mozilla.org/firefox/all as you basically just untar the tarbal and run the firefox script for the basics.