Rated 5 out of 5 stars

IT WORKS WITH THUNDERBIRD 60.* !!!!!!

Just download the AddOn, rename it from .xpi to .zip and open the zip-file
inside the archive is a file called "install.rdf", open it with any text-editor (wordpad, editor, etc.)
look for the line with
<em:maxVersion>53.*</em:maxVersion>
and change it to
<em:maxVersion>61.*</em:maxVersion>
save the file and repack the archive
At the end rename the archive back to the extension .xpi and install it manually with thunderbird

This review is for a previous version of the add-on (11.0.4.1). 

You can do that, but it doesn't mean that the add-on will work totally fine. The first thing I did when TB60 was released is to upgrade the compatibility number in the install.rdf file to check my add-on. This time I found it is too buggy, some icons are missing and the code came to the point that it is simply too bloated.

In addition, I would like to make use of CSS variables to make it a tad easier to maintain/edit my add-on and I also would like the theme's icons to support HDPI displays, since how this kind of screens are more and more popular. And finally, I would like to add official support for MacOS platform.

That's for all the reasons mentioned above that my addon's code needs a substantial refresh.

So edit the install.rdf file if you want, but keep in mind what I wrote above.