Add-ons

RequestPolicy by Justin Samuel

Be in control of which cross-site requests are allowed. Improve the privacy of your browsing by not letting other sites know your browsing habits. Secure yourself from Cross-Site Request Forgery (CSRF) and other attacks.

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

Thunderbird Message Filter Import/Export Enhanced by kounavi

Thunderbird Message Filter Import/Export Enhanced is a compatibility port of Wind Li's add on.
Original add on here: https://addons.mozilla.org/en-US/thunderbird/addon/thunderbird-message-filter-imp/

Hide Local Folders by Alex Cabal

Removes the "Local Folders" entry from the folder pane.

Unified Search by IagoSRL

Unify the global search box and the quick filter box in a new widget (the 'Unified Search Widget') with all filter and search capabilities at once.

Extra Folder Columns by Joey Minta, Thunderbird Development Team

This extension is for those TB3 users who want the multiple-columns view that TB2 allowed

IMPORTANT: If you are using Thunderbird 38 or later, uninstall this addon. The functionality is in core now.

Message Notes Plus by alehro

Message Notes Plus allows to add notes to emails. The notes don't affect the email in any way.They are stored locally on your hard drive.
The commercial version is no longer available. More info on mnpforum.alehro00.com and forum.alehro00.com.

Keyword Search by Mike Kaply

Search in the address bar without changing your search engine.

Firefox B light footer by NeHoMaR

Thunderbird B by Panther7