Rated 5 out of 5 stars

Very useful, many thanks!

It would be great if in addition to the button you could also use a keystroke, for example the letter "H" to activate the function.

This review is for a previous version of the add-on (5.1). 

With the key combination Ctrl + Alt + F5 you call the function of the button (the function depends on the options). Simpler keyboard shortcuts are already used by Thunderbird itself.