Garrett LeSage and a group of other good people have completed a nice upgrade of the Tango theme for Firefox 2. The theme brings the icons from the Tango Desktop Project to Firefox along with many improvements in making Firefox look and feel more like a native application on Linux.
There are also a series of “sub-themes” as well. The Gnome sub-theme matches with the default Gnome icon theme, Tangerine matches with the Ubuntu theme, and Industrial for the old Industrial Gnome theme.
Highly recommended for those using Firefox on Linux. There are rumblings of an update for the Tango theme for Thunderbird 2 as well.