Rated 4 out of 5 stars
Brings back old behaviour of Thunderbird 220.127.116.11 and makes live much easier.
Giving only four stars though, because pressing Escape not only closes the message window but does also reset quick filter (if string had been entered in quick search form before) or hide quick filter bar (if currently no string in search form).
I fixed this in my installation of the add-on by adding the following line after line 20 in file "messenger-overlay.js":
I hope the author will also apply this simple one-line-patch patch in the near future to make it available even to those who do not know how to alter the installation files.
New version is on its way :)