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Provider for Google Calendar

Allows bidirectional access to Google Calendar

Rated 3 out of 5 stars (1,659)
176,739 users

British English Dictionary (Marco Pinto)

A fork of Mark Tyndall's add-on, based on David Bartlett's
British Dictionary R1.19 for Firefox, Thunderbird and SeaMonkey.

V3.3.6 has 140 000+ new words and also fixes.

Rated 5 out of 5 stars (83)
158,828 users

English United States Dictionary

English United States (en-US) Dictionary as shipped with Thunderbird 115 ESR and Firefox 115 ESR.

Rated 4 out of 5 stars (39)
62,700 users

German Dictionary

German Dictionary (new Orthography) for spellchecking in Mozilla products

Rated 4 out of 5 stars (83)
241,467 users

Spanish (Spain) Dictionary

Spanish/Spain Dictionary

Rated 4 out of 5 stars (167)
54,735 users

Mail Merge

Create and Save or Send Multiple Individual and Personalized Messages from a Draft

Rated 5 out of 5 stars (231)
66,169 users

DKIM Verifier Featured

Verifies the DKIM-Signature of an e-mail.

Rated 4 out of 5 stars (49)
20,603 users

Dizionario italiano

Add support for Italian to spellchecking

Rated 4 out of 5 stars (71)
72,589 users

Send Later

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

Rated 5 out of 5 stars (264)
101,644 users

Woordenboek Nederlands

Dutch dictionary with wordslist from OpenTaal.

Rated 3 out of 5 stars (70)
23,557 users

Thunderbird Conversations Featured

This addon provides a conversation view for Thunderbird, grouping messages together and allowing you to reply "inline" thus providing a more efficient workflow.

Rated 4 out of 5 stars (570)
24,297 users

Signature Switch

Switch the signature on/off or choose a new one from your predefined set.

Rated 4 out of 5 stars (273)
50,862 users

Lightning Calendar Tabs

Displays tabs which allows quick navigation between time periods in Lightning calendar. All views of calendar are supported. Color of tab texts can be adjusted.

Rated 4 out of 5 stars (25)
25,233 users

Diccionario español Argentina

Spanish dictionary for Argentina.

Rated 4 out of 5 stars (93)
12,414 users

QuickFolders (Tabbed Folders)

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 (190)
14,344 users

Ukrainian dictionary

Ukrainian (uk-UA) spellchecking dictionary

Rated 5 out of 5 stars (58)
8,796 users

General Catalan dictionary

Free Catalan (general version) spelling dictionary.

Rated 4 out of 5 stars (40)
11,721 users

Canadian English Dictionary

For some reason, Mozilla doesn't have a Canadian localization team, but I know that even the British dictionary doesn't quite cut it for the truly patriotic.

Rated 4 out of 5 stars (82)
9,025 users

Emoji

Add emojis to your e-mails.

Rated 4 out of 5 stars (64)
24,074 users

Addressbooks Synchronizer

Synchronizes selected addressbooks with other instances of thunderbird
using local files, webdav servers or imap servers

Rated 4 out of 5 stars (81)
24,118 users