14 DAY TRIAL // 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.
Mozilla Firefox 9.0 brings features such as a Type Inference to radically improve JavaScript performance, Do Not Track status can now be queried via JavaScript, font-stretch support was added, text-overflow support was improved, HTML5, CSS, and MathML support was improved, various stability issues were fixed.
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.