Rated 5 out of 5 stars
Love this add-on. It frequently helps me avoid addressing mistakes.
I've posted a updated and fixed version which is compatible with Thubderbird 60.2.1 at the link below.
Just a warning: ALWAYS be careful about installing plugins from other websites! (You can open the plugin up and compare it with the original if you'd like to verify the changes I've made.)
If you have other fixes/changes to add then let me know on github.