Minutes ago I posted an update to the Better Gmail 2 Firefox extension, adding a new feature and cleaning out the redundant items that are available in Gmail Labs.
My favorite addition to this new version 0.7.3 is the awesome Unread Message Count in Favicon script, which adds that helpful little red unread message count to your Gmail tab's favicon (shown above). Note: A similar script which includes chat alerts is Gmail FavIcon Alerts, which I'll try to get permission to include in future Better Gmail 2 versions.
Download the latest version of the extension from the Better Gmail 2 homepage and check out the changelog for the nuts and bolts of what was added, removed, and updated.
Better Gmail 2 [Lifehacker Code]
Better Gmail 2 Gets Unread Message Favicon (and Cleaned Up) [Smarterware]