Rated 2 out of 5 stars

It makes what claims, but if by mistake you open another window, it will not close...

This review is for a previous version of the add-on ( 

This issue has been fixed in version, which is awaiting its review by the Thunderbird add-ons team since about a month now. If you don't want to wait for the review, you can download it at https://addons.thunderbird.net/thunderbird/downloads/file/1016729/minimize_on_close-