Rated 5 out of 5 stars

Από τον/την sberg43 στις Αύγ. 15, 2010 · μόνιμος σύνδεσμος

I too was unable to use this add-on after the update to Thunderbird 3.1.2. A nice replacement is "MinimizeToTray revived"
https://addons.mozilla.org/en-US/thunderbird/addon/12581/

(My rating is for the new add-on)