by conema (Developer) on Nov. 16, 2020 · permalink

Sadly, I think that I can't do anything about it, full themes are no more supported and I'm using an official "experimental" API, which gives me a way to make full themes compatible with the last versions of Thunderbird. I think that this API is why you are seeing that "full access" message. Also, you can verify that a lot of addons in the store asks for "full access", probably for the same reason.

The theme is open source and it isn't obfuscated in any way, thus you can easily see that it doesn't do anything bad and the only permission really used is the storage one (https://github.com/conema/monterail-dark/blob/master/manifest.json under "permissions"), which is needed to save the folderTreeHeight and messageListHeight. The theme is composed of CSS files and JS files, in particular the js files in "api/WindowListener" are the official "experimental" APIs of thunderbird, so nothing bad happens here; the other JS files are located in "content/scripts/" and these files simply inject the CSS files in Thunderbird and you can easily verify that also nothing bad happens here. Furthermore, remember that each time I upload a new version of the theme, it's checked by the TB admins.

If you have any advices or you want to continue the discussion, feel free to open an issue on the github repo.