Rated 5 out of 5 stars

I assume the add-on works just fine, but before installing it, a simple question - why does it need a permission to "Have full, unrestricted access to Thunderbird, and your computer"? What does it mean?

This review is for a previous version of the add-on (2.16). 

With TB78 the extension system changed towards MailExtensions which only allow access to TB via a subset of APIs. Those APIs are currently not enough to build TbSync. I therfore use a special API which gives me full access like I had with legacy extensions in TB68.