Up & Coming Extensions
LookOut Requires Restart
LookOut is a plugin which allows Thunderbird to interface with Microsoft's mail tools by decoding metadata and attachments encapsulated/embedded in a TNEF encoded attachment (aka winmail.dat).
Reinstates the extensions.checkCompatibility preference without respect to the current application version.
MinimizeToTray revived Requires Restart
Minimizes windows into the system tray.
ImportExportTools Requires Restart
Adds some tools to import and export folders and messages
FireTray Requires Restart
A system tray extension for Linux and Windows, allowing to set up custom icon, hiding to tray instead of closing, display the number of unread messages in mailing applications, and other features ...
As of Firefox 33, Venkman *no longer works*, as the APIs which it needs have been removed.
Join-NG Requires Restart
Join partial messages. Somewhat similar to MS Outlook Express "combine and decode".