Organize your schedule and life's important events in a calendar that's fully integrated with your Thunderbird email. Manage multiple calendars, create your daily to do list, invite friends to events, and subscribe to public calendars.
Allows bidirectional access to Google Calendar
Use the Evernote Web Clipper to save things you see on the web into your Evernote account.
United States English Spellchecker for Firefox, Thunderbird and SeaMonkey by Kevin Atkinson and Geoff Kuenning.
To enable, right-click in a multi-line text box, select "Languages", then "English (United States)".
This addon provides a conversation view for Thunderbird, grouping messages together and allowing you to reply "inline" thus providing a more efficient workflow.
The latest version is compatible with Thunderbird 38+ only (see below for details).
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.
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
URL Link is a small Firefox and Thunderbird extension that allows you to select a non-URL in a mail/news message or web-page, and open it in a browser window.
Search and remove messages which are the same as other messages in your mail folders (referred to as duplicates or dupes).
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!
Clip to OneNote is a free add-on which helps you to send text, pictures and other data to Microsoft Office OneNote with a single click.
Thunderbird Message Filter Import/Export is a thunderbird/mozilla extension to import/export message filters.
Quickly get to the latest nightly build of Lightning relevant to the version of Thunderbird and the OS you're on.