Some possible improvements Rated 4 out of 5 stars

Nice and useful add-on!Maybe for further improvement:- when switching to another screen (within Thunderbird), while that particular message still selected, the note keeps visible. As a matter of fact, while I'm writing this posting, the note still is visible in this window (a separate Tab)- when adjusting width and hight to a smaller appearance, the text runs out of space en the right part of it disappearing.

This review is for a previous version of the add-on (2.2.6).