Rated 4 out of 5 stars
This is a great add-on. I used it several months but I noted that I could not open messages with double click.
Today I disabled all add-ons and re-enabled them once by once and found that it is Copy Attachment to Clipboard.
What a pity. I really like this add-on but disabled it for now.
The add-ons is dead I suppose because the owner hasn't resolved this problem over several months.