birdtray
nifty little trayicon for thunderbird that changes colour when new email arrives, alternatively flashing icon or new mail count. also allows tbird to minimize to tray and a few other things (see homepage). in short its basically a replacement for the old tbird extension called firetray that no longer works because mozilla changed something, except birdtray is a standalone app, not an extension and immune to changes to tbird

GPLv3

https://github.com/gyunaev/birdtray
https://github.com/gyunaev/birdtray/archive/RELEASE_1.7.0.tar.gz