X-FOAFheader. Phil Wilson took the MessageFaces source code and modified it for
X-FOAF. Woohoo, Phil!
Meanwhile, Chris Schmidt has released and announced Thunderbird FOAF. It, too, is based on existing code.
A big thanks to Jens Bannmann, who created the MessageFaces extension. He outlines the difficulties of working with Thunderbird headers in extensions:
Just to warn you: There are a few obstacles here. The first is that
unless the user sets "View all headers", only the standard headers are
sent to the UI. Unfortunately, the set of headers is hard-coded into
the core (see https://bugzilla.mozilla.org/show_bug.cgi?id=236954 for
future work to change this).
To work around this, MessageFaces has a mechanism to switch the All
Headers preference on just before the message is loaded, and to switch
back before it actually gets displayed. This is a really, really
fragile hack, but we have to live with it.
The second problem is that the Enigmail extension does this, too, and
would collide with the MessageFaces hack. However, MessageFaces
detects when Enigmail is present, and does not activate its own hack
then. You'd have to do the same for your extension (make sure neither
Enigmail nor MessageFaces is present, and only then activate the
The third problem is that you should *not* meddle with the header pref
when the message pane is not displayed, as it would break the second
instance of your extension that's started in the separate message
As Phil put it, "Jens is the dude."
Thunderbird (email client) as FOAF killer app?