Rated 4 out of 5 stars

From time to time, the tray icon does not restore Thunderbird when clicked. Minimizing all open windows (by clicking Show desktop) makes click-to-restore work again.
Tested with Minimizetotray 1.3.2, Thunderbird portable 45.6.0 on Windows 10 Anniversary update. It behaved the same with an older Thunderbird portable and older add-on version.