My favorite and some localized add-ons for Thunderbird, Sunbird/Lightning.
Add Dropbox support to Thunderbird's Filelink feature.
Walnut2 for Thunderbird, based on icons from art.gnome.org. Walnut2 is based on Walnut but with better looking wood panels. Fully compatible with from 5.0 upto latest nightly build (currently 27.0a1). Full support for Lightning/calendar.
Collector's Note 木目調のテーマ。
Add as many local folders as you want to (like outlook PST).
NB. It doesn't import PST files.
Thunderbird Message Filter Import/Export is a thunderbird/mozilla extension to import/export message filters.
Collector's Note メッセージフィルタのインポート/エクスポート。日本語改造版。http://www.geocities.jp/chimantaea_mirabilis/filtersimportexport/index.html
Displays icon for user agent of received mails.
Collector's Note 開発用。
This Add-on allows to have HTML temporarily allowed in the currently displayed message by only one click. When switching to another message, it'll be shown automatically again in plain text or simple html mode (if this is your default mode).
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。
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.
Export/Import Account Settings.....
Collector's Note アカウント設定のインポート/エクスポート。
Adds a new action to mail filters to allow playing a particular sound when the filter matches. Also includes several sample sound files.
Collector's Note メッセージフィルタで受信音を設定できる。
Adds the possibility to use a WebDAV store for Filelink. With this extension you can link attachments to a WebDAV service, for example as provided by Apache's mod_dav or some public services.