Rated 3 out of 5 stars

I am very glad, that someone reimplemented this neccessary addon.

But I also kindly like to ask, why the addon needs full access on thunderbird and my computer?

This review is for a previous version of the add-on (1.0.0). 

Addons can either use built-in APIs (new in TB68, severly limited functionality, but with fine-grained permissions) or directly interact with Thunderbird (as powerful as pre-TB68 addons, but without any permission control).

Currently there is no API to modify or extend message list view, so only way to achieve this functionality is via direct interaction, which requires full access.

Feel free to grab the addon source from github, review it (it's tiny) and install it from local copy. I'm afraid there is no way for me to prove addon is safe and I can't change required permission level.