DancingMouse brings Tango icons to Mozilla Firefox. It supports many Firefox extensions: All in One Sidebar, Sage, Image Toolbar, Tab Mix Plus, Pearl Crescent Page Saver Basic and FireFTP. Support of other extensions is planned.
Enjoy! You can also try DancingMouse for Thunderbird! http://gnome-look.org/content/show.php/DancingMouse+for+Thunderbird?content=57646
(I know that lots of Tango-based Firefox themes exist now, but no one meet my needs...)
Thank you for your comments and ideas.