Add-ons

Provider for Google Calendar by Philipp Kewisch

Allows bidirectional access to Google Calendar

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).

Google Calendar Tab by Bryan Clark

Adds the Google Calendar web interface as a new tab directly into Thunderbird. Creating and viewing events works just as it would in a browser like Firefox

Toolbar Buttons by Button Guy

Adds toolbar buttons to the customize toolbar window in several programs including Firefox, Thunderbird and SeaMonkey. Some of the buttons make commonly preformed actions quicker, others add new functionality.

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).

Compact Menu 2 by Milly

Add a compact menu button to the navigation toolbar, and hide the menu bar.

Keyword Highlight by genta

Keywordhighlight changes color/size/weight of your favorite keywords...

SendVia by double-six

Sometimes you need to select a specific SMTP server for sending the current message? Then SendVia is for you.

SendVia provides the `Send' button of message composition windows with a drop-down menu from which you can select or create the SMTP server...

gassiribird by miyase