Organize your schedule and life's important events in a calendar that's fully integrated with your Thunderbird email. Manage multiple calendars, create your daily to do list, invite friends to events, and subscribe to public calendars.
Allows bidirectional access to Google Calendar
OpenPGP message encryption and authentication for Thunderbird and SeaMonkey.
Access to Google contacts and synchronize them with Thunderbird address books.
Allows you to quickly switch to a different language (User Interface, Spell Checker Dictionary and Website content) in your Mozilla application.
Switch the signature on/off or choose a new one from your predefined set...
Synchronizes contacts & groups between Thunderbird or SeaMonkey and Google Contacts. Imports Facebook friends, contacts you follow on Twitter, and more.
Allow to redirect (a.k.a. "bounce") mail messages to other recipients
Did your friend send you a cool link? Want to read the rest of that interesting article? Don't want to open up your web browser just to view it? You don't have to! Just view it in Thunderbird with ThunderBrowse!
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.
If you have duplicate messages (e.g. from merging folders or downloading messages several times) you can use this tool to find and remove them from the selected folder and its subfolder by rightclicking on a folder and choosing "Remove duplicates..."
Allows for customization of the folder pane. Accounts can be rearranged and the startup folder can be chosen.
URL Link is a small Firefox and Thunderbird extension that allows you to select a non-URL in a mail/news message or web-page, and open it in a browser window.