Rated 5 out of 5 stars

Thunderbird v52 install seems to have killed this add-on. Not a complaint. Just FYI. I reverted back to v45 and the add-on is working flawlessly as before. Wonderful tool to have! Thank you!

This review is for a previous version of the add-on (1.9.0). 

I'm already looking into it and hope to release a fix this week.
Thank you for reporting because I wasn't aware of it. And thanks for the 5 stars review!

Update: Published new version that fixes compatibility with v52.