Rated 4 out of 5 stars

Would be 5 stars .. all it needs is an option to display the envelope sender (aka "MAIL FROM" or "Return-Path:")

Unfortunately, it seems a trivially to fix bug in Thunderbird (no surprise nobody fixed it yet) prevents this from being possible.

https://bugzilla.mozilla.org/show_bug.cgi?id=494100

This review is for a previous version of the add-on (0.1.9).