ImportExportTools Requires Restart
Adds some tools to import and export folders and messages
Fight the text ads! Element Hiding Helper is a companion extension for Adblock Plus meant to make creating element hiding rules easier.
Provider for Google Calendar Requires Restart
Allows bidirectional access to Google Calendar
If you are the kind of person who likes to have total control over every aspect of your downloads, "Download Status Bar" is the add-on you are looking for.
SQLite Manager Requires Restart
Manage any SQLite database on your computer.
MinimizeToTray revived Requires Restart
Minimizes windows into the system tray.
Add-ons Manager Context Menu Requires Restart
Add more items to Add-ons Manager context menu.
Quicktext Requires Restart
Quicktext is an extension for Thunderbird that lets you create templates that can be easily inserted into your own emails.
UnMHT allows you to view MHT (MHTML) web archive format files, and save complete web pages, including text and graphics, into a single MHT file in Firefox/SeaMonkey.
As of Firefox 33, Venkman *no longer works*, as the APIs which it needs have been removed.
DOM Inspector Requires Restart
DOM Inspector is a tool that can be used to inspect and edit the live DOM of any web document or XUL application. The DOM can be navigated using a two-paned window displaying a variety of different views on the document and all nodes within.
Google Calendar Tab Requires Restart
Adds the Google Calendar web interface as a new tab directly into Thunderbird. Creating and viewing events works just as it would in a browser like Firefox
Mail Redirect Requires Restart Uitgesoek
Allow to redirect (a.k.a. "remail") mail messages to other recipients.
PrintingTools Requires Restart
Adds some options to print messages and addressbooks
Display Quota Requires Restart
This extension will display the current status of your IMAP quota in thunderbird's statusbar and will warn you when you reach a configurable limit...
'Classic Toolbar Buttons' add-on restores old toolbar button ui (known from Fx 4-7s small view, Fx 4-12s large view & Tb 5-14) for current Firefox, Thunderbird and Seamonkey versions.
Beta builds on versions page!
Copy Plain Text 2 Requires Restart
Copies text without formatting
"Restart" menu and button, with configurable shortcut key.
Firefox and Thunderbird extension to manage user preferences and user profile CA certificates using group policy
Font Finder Requires Restart
FontFinder is created for designers, developers and typographers. It allows a user to analyze the font information of any element on a page, copy any piece(s) of that information to the clipboard, and perform inline replacements to test new layouts.