Ubuntuzilla can integrate the new version of Firefox into your system as well as undo its changes if you want to go back. All your extensions, bookmarks, plugins, and settings should transfer over to the new version. The only thing that didn’t transfer was my open tabs from my previous session.
Ubuntuzilla will ask a few questions: confirming that it has found the correct version to install, choosing a localization (14 for en-US), confirming the localization, a sudo prompt, and a prompt for enabling automatic updating. Near the end of the process you should see The new Firefox version 3.5 has been installed successfully.
You can now use your normal Firefox item in the menu to start Firefox 3.5, or by running the command firefox. Check out Ubuntuzilla’s website for the simple removal instructions as well as what do do when you are notified there is a Firefox update available.