Thunderbird extensions and add-ons

[urukrama]

In another thread (http://ubuntuforums.org/showthread.php?t=1699212) many of you stated Thunderbird to be your favourite mail client, and several of you mentioned it's add-ons as one of its strengths.

What add-ons do you use and/or recommend?

[Habitual]

Engimail
Lightning
Firetray

[cariboo]

I use Enigmail and xul-ext-lightning (Lightning) extensions for Thunderbird