Rated 5 out of 5 stars

Amazing, works well.

However, the "Have full, unrestricted access to Thunderbird, and your computer" seems exaggerated, please request only required permissions and this would be perfect. (edit: see answer).

Also, it keeps asking (edit: not anymore) me "It looks like you wrote this email in Markdown but forgot to make it pretty. Send it anyway?", even when I just did make it pretty.

Edit (reply):
Thanks for the explanation on the permission, fair enough. Also I do not have false positive anymore, I don't know why, but good. So all good, thanks for the work.

This review is for a previous version of the add-on (3.1.1). 

I updated the description with the reason for the "unrestricted access" permission. Mail extension APIs are evolving, and my expectation is that the missing API or one that accomplishes the same thing will be added in a future Thunderbird version.

I have not had many false positives with the markdown detection, but not too many. If you have a sample message that incorrectly triggers the notification, please file a bug on the Gitlab page.