As of Firefox 33, Venkman *no longer works*, as the APIs which it needs have been removed.
DirSwitcher Requires Restart
Change direction in compose...
View Headers Toggle Button Requires Restart
This extension adds a toolbar button that allows the easy toggling of viewing all message headers.
StockTicker Requires Restart
Shows your favorite stocks in a customizable...
Quote Colors Requires Restart
Quote Colors allows you to select text and background colors of different quote levels which are applied when reading or printing mail/news messages. Additionally, you can choose between graphical and traditional plain text quoting display mode.
addressContext Requires Restart
An extension to add addressbook-related options to the context...
Show SMTP Username Requires Restart
Displays username (if available) next to SMTP...
Delete Junk Context Menu Requires Restart
Adds 'Delete Mail Marked as Junk' to folders' right click...
Moji Requires Restart
An integrated sidebar-dictionary for Japanese and Chinese including kanji dictionary.
Image Zoom Requires Restart
Adds zoom and rotation functionality for images...
Copy Plain Text Requires Restart
Copies text without formatting...
Forumzilla Requires Restart
Forumzilla lets you read news and blog feeds in your email application. It is similar to the feed reader built into Thunderbird, but it lets you download stories into any folder in any POP, IMAP, or local account (configurable per...
Open Long Url Requires Restart
Adds an option to your File menu to allow you to open long, multi-line...
Easy Get Mail Button Requires Restart
Makes the 'Get new messages' button context-sensitive. Select an account root folder to get messages for that account, any other folder to get messages for all...
Buttons! Requires Restart
Adds buttons to the Thunderbird toolbars such as Next! and Previous! buttons for navigating through all messages instead of just unread ones. See homepage for more...
Launchy Requires Restart
Launchy will enable you to open links and mailto's with external applications...
OpenPGP message encryption and authentication for Thunderbird and SeaMonkey.
Contacts Sidebar Requires Restart
Displays the address books in a sidebar in Thunderbirds 3-pane-window and can be toggled with the F4 key or a toolbar button.
Visit my Contacts Sidebar site for recent versions and news.
InspectorWidget Requires Restart
Adds toolbar button and context menus for invoking the DOM Inspector (DOMi) for either chrome or content elements.
QuickNote Requires Restart
A simple note-taking extension.