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FolderFlags Requires Restart

Allows users to edit the flags Thunderbird sets on folders.

Rated 5 out of 5 stars (8)
3,455 users

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.

Rated 4 out of 5 stars (11)
2,086 users

ThunderBirthDay Requires Restart

Display birthdays from the Thunderbird addressbooks as events in Lightning.

Rated 4 out of 5 stars (78)
14,294 users

Mail Merge Requires Restart

Mass Mail and Personal Mail

Rated 5 out of 5 stars (159)
62,549 users

Year view Requires Restart

Year view for calendar.

Rated 4 out of 5 stars (49)
3,446 users

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.

Rated 4 out of 5 stars (33)
7,830 users

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.

Rated 5 out of 5 stars (52)
17,467 users

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.

Rated 5 out of 5 stars (2)
1,953 users

Send Later Requires Restart

True "Send Later" functionality to schedule the time for sending an email.

Rated 5 out of 5 stars (116)
70,563 users

Provider for Google Calendar Requires Restart

Allows bidirectional access to Google Calendar

Rated 4 out of 5 stars (972)
330,726 users

ImportExportTools Requires Restart

Adds some tools to import and export folders and messages

Rated 4 out of 5 stars (181)
468,139 users

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!

Rated 5 out of 5 stars (121)
21,632 users

Remote XUL Manager

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.

Rated 5 out of 5 stars (36)
92,805 users

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.

Rated 4 out of 5 stars (39)
6,382 users

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.

Rated 4 out of 5 stars (27)
5,595 users

ThreadKey

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

Rated 4 out of 5 stars (23)
1,512 users

Simple Locale Switcher Requires Restart

An easier management of the user interface language

Rated 5 out of 5 stars (14)
31,133 users

IMAP Received Date Requires Restart

Make the “Received” column in IMAP folders show when messages were actually received.

Rated 5 out of 5 stars (11)
2,299 users

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).

Rated 3 out of 5 stars (26)
8,307 users

gContactSync Requires Restart

Synchronizes contacts & groups between Thunderbird or SeaMonkey and Google Contacts. Imports Facebook friends, contacts you follow on Twitter, and more.

Rated 4 out of 5 stars (239)
92,200 users