Rated 5 out of 5 stars

A good extension, working as expected.

However, I did not find a button to minimize Thunderbird to tray
(this feature could be added)

Another feature request : the tray icon might be shown ONLY when the main window is hidden
(instead of always or never)

Minor bug : when installed in Thunderbird the tray tooltip says "Firefox..." instead of "Thunderbird..."

Thanks for the developper nevertheless.