Add-ons

Provider for Google Calendar by Philipp Kewisch

Allows bidirectional access to Google Calendar

Enigmail by Patrick Brunschwig

Helper tool to migrate your keys and important settings from Enigmail to Thunderbird 78.

Mail Merge by Alexander Bergmann

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

LookOut by Aron Rubin

LookOut is a plugin which allows Thunderbird to interface with Microsoft's mail tools by decoding metadata and attachments encapsulated/embedded in a TNEF encoded attachment (aka winmail.dat).

Remove Duplicate Messages by Eyal Rozenberg

Search and remove messages which are the same as other messages in your mail folders (referred to as duplicates or dupes).

Mail Redirect by Onno Ekker, Pawel Krzesniak

Allow to redirect (a.k.a. "remail") mail messages to other recipients.

Collector's Note 日本語改造版。http://www.geocities.jp/chimantaea_mirabilis/mailredirect/index.html

CompactHeader by jmozmoz

Add symbol in header plane to switch between compact and expanded view. Work only for Thunderbird 68.0 and older. Currently, there are no plans to update this for newer versions.

Collector's Note Thunderbird 3 用のメッセージヘッダの表示をカスタマイズするアドオン。

QuickFolders (Tabbed Folders) by Realraven (Axel Grude), Alexander Malfait

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!

Stationery by Arivald

Extension to mimic Outlook Express Stationery.
Allow you to use HTML files as templates for mail. Also allow custom template in replies or forwarded mail!

Collector's Note メッセージのひな形管理。

Walnut2 for Thunderbird by alfredkayser

Walnut2 for Thunderbird, based on icons from art.gnome.org. Walnut2 is based on Walnut but with better looking wood panels.
Supports Thunderbird versions 53.0 to 60.0. From version 61.0, Thunderbird will drop support for full custom themes.

Collector's Note 木目調のテーマ。

Google Contacts by H.Ogi

Access to Google contacts and synchronize them with Thunderbird address books.

Allow HTML Temp by Alexander Ihrig

Allows to have HTML temporarily enabled (and displayed) in the currently selected message by only one click. When switching to another message, it'll be shown automatically again in plain text or simple html mode (according to your settings).

Quote Colors by Malte Ruecker

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.

Provider for Microsoft Exchange by Simon Schubert

The lightning-exchange-provider addon allows you to use Microsoft Exchange calendars in Thunderbird, via Exchange’s web services.

This addon only works with Microsoft Exchange 2007 and above. Exchange 2003 is not supported.

Nostalgy by Alain Frisch

Keyboard shortcuts to change folder, move/copy messages, with folder name auto-completion.

Collector's Note キーボードショートカットでメッセージ操作できる。