Firefox 9 Officially Lands in Ubuntu 11.10
Oneiric Ocelot users can now update to Firefox 9 via official channels
A few days ago, Canonical uploaded the final bits of the Mozilla Firefox 9.0 web browser on the official software repositories for the Ubuntu 11.10 (Oneiric Ocelot) operating system.All Ubuntu 11.10 and Ubuntu 11.04 users can now upgrade (by running the Software Update app from the Settings icon) their default web browser to Firefox 9.0, which was officially released by Mozilla three weeks ago, on December 19th, 2011.
Keep in mind that after the upgrade, you have to restart any running instances of Firefox. Also, if you want to install Firefox 10.0 on Ubuntu 11.10, follow this tutorial.