Mail Merge Requires Restart Featured
Create and Save or Send Multiple Individual and Personalized Messages from a Draft
Mail Redirect Featured
Allow to redirect (a.k.a. "remail") mail messages to other recipients.
OpenPGP message encryption and authentication for Thunderbird and SeaMonkey.
CompactHeader Requires Restart Featured
Add symbol in header plane to switch between compact and expanded view. Options to switch between one or two lines compact view, which buttons should be displayed in header pane. New beta version available from http://compactheader.mozdev.org/