Rated 4 out of 5 stars

per Ray Stevens el gen. 15, 2010 · enllaç permanent

As mentioned below, I have a simple hack that enables this for TB 3.0.

To get a copy of rev 0.7.1 with the hack, go to:
http://forum.addonsmirror.net/index.php?showtopic=1906&st=0&gopid=38064&#entry38064

I rate this 4 stars -- I'd love to see this built into Thunderbird itself.

Usage note: look for "Change Header Details" in the Message pulldown menu from the main toolbar.