Rated 5 out of 5 stars

I know The Ripper explains why they stopped maintaining and updating this Add-On by saying: "I stopped maintainig this AddOn, because in current Thunderbird Versions the "Reply" Button has a Dropdown, that shows all emailadresses that Thunderbird finds in this email."

...but unfortunately this is no longer True. In Thunderbird 52 I cannot find any such drop-down on the reply button.

We need this add-on once again! It would not be redundant! :)

EDIT 2018-04-09
No, I don't see the small downward triangle under any reply button. tested on Thunderbird 52.7.0 on Mac, and on Linux, and on Windows. I tried both the reply button by the message headers, and the optional reply button that can be added to the top toolbar. I tried with no add-ons/extensions installed. I even tried creating a new profile with thunderbird.exe -profilemanager and there was still no sign of the little downward triangle.

I am on Thunderbird 52.7 and beneath my reply button there is a small downward triangle. If I am opening this, I get a list of email adresses I could select to reply to.
Do you have it again visible on your installation or ist there something wrong with your configuration?