Rated 3 out of 5 stars

Doesn't seem to do anything (TB 60.6.1 on macOS 10.14.4)

EDIT: to be more precise, this add-on conflicts with the Display Mail User Agent extension for Thunderbird. When that is installed, Autocopy doesn't work.
See http://www.juergen-ernst.de/addons/dispmua.html

Updating my rating to 3.

Sorry, but I just repacked and upload here the old extension with a little mod stated from here http://forums.mozillazine.org/viewtopic.php?f=39&t=3041270&start=90
Beyond that I don't have the skill to fix that or anything else. This addon is going to stop on the next big version of TB unfortunately.