Minimize to system tray (Thunderbird)
From MozillaZine Knowledge Base
Thunderbird cannot minimise itself to the system tray. However, users of Microsoft Windows can try using one of the utilities mentioned in this thread, this thread or this thread for minimising Thunderbird to the tray.
If you use GNOME, you can (like with any mail program, or even without one) add the Inbox Monitor applet to your panel, and configure it to launch Thunderbird upon double-click; however, each monitor can only watch one email account.
