Up & Coming Extensions
FolderFlags Requires Restart
Allows users to edit the flags Thunderbird sets on folders.
Personal Level Indicators Requires Restart
Shows an indicator so you can tell if an email was addressed only to you (»), a group (›), or a mailing list.
ThunderBirthDay Requires Restart
Display birthdays from the Thunderbird addressbooks as events in Lightning.
Mail Merge Requires Restart
Mass Mail and Personal Mail
Year view Requires Restart
Year view for calendar.
Shrunked Image Resizer Requires Restart
Make your photos smaller, so they don't take forever to email or send to websites.
This extension is not being converted to a WebExtension.
SmartTemplate4 Requires Restart
SmartTemplate4 offers an easy way to automatically create customized replies by auto-inserting various mail headers. Templates can be created for every account as well as for the default (all email accounts). Also supports the Stationery Add-on.
Quick Locale Switcher 2 Requires Restart
Allows you to quickly switch to a different language (User Interface, Spell Checker Dictionary and Website content) in your Mozilla application.
Send Later Requires Restart
True "Send Later" functionality to schedule the time for sending an email.
Provider for Google Calendar Requires Restart
Allows bidirectional access to Google Calendar
ImportExportTools Requires Restart
Adds some tools to import and export folders and messages
QuickFolders (Tabbed Folders) Requires Restart
The "Swiss army knife" of folders. Turn your favorites into tabs - open folders and subfolders, move mails without scrolling around or searching. powerful + easy.
See new mail at a glance after automatic filtering - supports quickFilters addon!
Manages the Remote XUL whitelist to allow websites and local files to load XUL content. For versions compatible with Firefox 41 and lower, see All Versions page below.
Lightning Nightly Updater (Unofficial) Requires Restart
Quickly get to the latest nightly build of Lightning relevant to the version of Thunderbird and the OS you're on.
QuoteCollapse Requires Restart
Collapse and expand quotes. Please see the extension homepage for further information.
Note that MozDev has shut down long ago (mailing list etc). Add-On homepage, source code and issue tracker are on GitHub, as linked on this page.
Strike the 'T' key to sort messages by thread, strike the 'U' key to sort them unthreaded again, just like the 'G' key switches to Grouped By Sort view
Simple Locale Switcher Requires Restart
An easier management of the user interface language
IMAP Received Date Requires Restart
Make the “Received” column in IMAP folders show when messages were actually received.
ConfigDate Requires Restart
ConfigDate allows to configure the "Date" column in message threadpane. When displaying the message header, it is possible to display the (default) formated date or the senders local sent time (Date-String).
gContactSync Requires Restart
Synchronizes contacts & groups between Thunderbird or SeaMonkey and Google Contacts. Imports Facebook friends, contacts you follow on Twitter, and more.