Rated 5 out of 5 stars

I just now known about this add-on.
Would like to use it, but I can't install it.
Not compatible with versions above 45. :(
Hope the developer updates it to be compatible with current versions.

[EDIT]
Was really easy to make it work, and work great, with my TB 52.3.

Do the following (this seems like a lot of steps, but I like to do all baby steps):
1. download the XPI
2. rename the .xpi to .zip
3. open it with 7-zip (or whatever you use to open zip files) extract the content to a folder.
4. open file install.rdf
5. change this line "<em:maxVersion>45.*</em:maxVersion> "to "<em:maxVersion>55.*</em:maxVersion>" (I changed it to 55 just to be safe for future updates of Thunderbird)
6. save the file install.rdf
7. from within the folder where the files are, select them all and make a zip with the defaults for "normal" compression.
8. rename the file from .zip to .xpi
9. and lastly follow the very simple instructions from mozilla on how to install a xpi as an extension (https://support.mozilla.org/en-US/kb/installing-addon-thunderbird#w_a-slightly-less-ideal-case-install-from-a-downloaded-xpi-file)

This is working great and its simple to use. It would benefit to have a little manual with many case examples for each potential use of the extension, since it looks simple but can be used in many places in many different ways.
But its not a requirement since the existing information on the authors site is enough to start using it.

I would like to point out another fact that made me give 5 stars.
I usually give 4, since there's always room for improvement: I sent a question to the author by email and... YES he answered and I sent another email and got another reply... WOW. He really is interested in helping and goes the extra step and gives nice replies.

Best regards to Kent James (from Portugal) and thank you for the work you put in this that is a great help to everyone here using it. :-)

Take care.

This review is for a previous version of the add-on (1.3.2).