Rated 3 out of 5 stars

It conflicts with the other Monterail themes. Can only have one Monterail theme installed at a time.

Also, when the thunderbird window is maximized in Windows 10, the tab/minimize/maximize/close titlebar is cropped.

Edit: I opened a new issue in the github link you sent me.

Léirmheas ar leagan níos sine den bhreiseán seo (1.1.2). 

A fix for compatibility issues between versions is being released, it will be out in a few hours, after it has been accepted by admin. Note that the new version of Thunderbird has a bug that compromises the normal working of themes, themes aren't applied, it can't be fixed by themes developers. This fix only resolved the bug that did not allow to activate one theme a the time, because everyone is activated together.

I can't reproduce your second problem, about the titlebar being cropped. I would be glad if the discussion continued in the support website linked on the right (https://github.com/conema/monterail-dark/issues), so we can discuss your problem better.