DancingMouse brings Tango icons to Mozilla Thunderbird.
Enjoy! You can also try DancingMouse for Firefox! http://gnome-look.org/content/show.php/DancingMouse+for+Firefox?content=56995
(I know that lots of Tango-based Thunderbird themes exist now, but no one meet my needs...)
Thank you for your comments and ideas.
Tasks for you:
Can you send me screenshots of icons of your mailboxes (Local Folders, etc.) in the left-side panel? The icon for Local Folders runs right, but I would like to know what icons are displayed for IMAP accounts and for "separate" account (= not in Local Folders). There were some problems; I don't know what the icon with the lock should mean, etc. Thank you very much!