Possible Duplicate:
How do I install Firefox 4?
Is the the packages still not out ?
Possible Duplicate:
How do I install Firefox 4?
Is the the packages still not out ?
The latest version of Firefox is available for as a security updates in all supported releases of Ubuntu, just doing a normal update will pull it in.
Usually it's available within a few hours of Mozilla's announcement, sometimes faster, depending on the archive builders, and the speed of your local mirror, etc.
You have to add the PPA ppa:mozillateam/firefox-stable
for the latest firefox.
Go to System -> Administration -> Update Manager -> Settings (Button) -> Other Software (tab) -> Add and then paste ppa:mozillateam/firefox-stable and Update.