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Remove Duplicate Messages (Alternate) Requires Restart

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

Rated 4 out of 5 stars (178)
72,267 users

LookOut (fix version) Requires Restart

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).
Support: Thunderbird and SeaMonkey

Rated 4 out of 5 stars (22)
71,829 users

UnMHT

UnMHT allows you to view MHT (MHTML) web archive format files, and save complete web pages, including text and graphics, into a single MHT file in Firefox/SeaMonkey.

Rated 4 out of 5 stars (298)
65,733 users

Image Zoom Requires Restart

Adds zoom and rotation functionality for images...

Rated 4 out of 5 stars (354)
65,547 users

Mail Merge Requires Restart Featured

Mass Mail and Personal Mail

Rated 5 out of 5 stars (159)
65,412 users

Saved Password Editor Requires Restart

Adds the ability to create and edit entries in the password manager.

Rated 5 out of 5 stars (387)
58,086 users

JavaScript Debugger Requires Restart

As of Firefox 33, Venkman *no longer works*, as the APIs which it needs have been removed.

Venkman is the code name for Mozilla's JavaScript Debugger. Venkman aimed to provide a powerful JavaScript debugging environment for Mozilla based browsers.

Rated 4 out of 5 stars (52)
57,135 users

DOM Inspector Requires Restart

DOM Inspector is a tool that can be used to inspect and edit the live DOM of any web document or XUL application. The DOM can be navigated using a two-paned window displaying a variety of different views on the document and all nodes within.

Rated 5 out of 5 stars (77)
54,230 users

Add-ons Manager Context Menu Requires Restart

Add more items to Add-ons Manager context menu.

Rated 5 out of 5 stars (49)
48,690 users

Google Calendar Tab Requires Restart

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

Rated 4 out of 5 stars (86)
42,852 users

Remove Duplicate Messages Requires Restart

If you have duplicate messages (e.g. from merging folders or downloading messages several times) you can use this tool to find and remove them from the selected folder and its subfolder by rightclicking on a folder and choosing "Remove duplicates..."

Rated 4 out of 5 stars (141)
40,442 users

Mail Redirect Requires Restart Featured

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

Rated 4 out of 5 stars (126)
39,549 users

ReminderFox Requires Restart

ReminderFox displays and manages lists of reminders and ToDo's. ReminderFox makes sure you remember all of your important dates via easy-to-use lists, alerts, and alarms, right in your browser without the need for a separate calendar program.

Rated 4 out of 5 stars (532)
39,214 users

Display Quota Requires Restart

This extension will display the current status of your IMAP quota in thunderbird's statusbar and will warn you when you reach a configurable limit...

Rated 4 out of 5 stars (30)
39,035 users

PrintingTools Requires Restart

Adds some options to print messages and addressbooks

Rated 5 out of 5 stars (25)
37,111 users

Addressbooks Synchronizer Requires Restart

Synchronizes selected addressbooks with other instances of thunderbird
using ftp/webdav/imap servers

Rated 4 out of 5 stars (59)
36,899 users

Bluhell Firewall

Get a faster browsing experience by blocking nasty web resources using Bluhell Firewall, the lightweight Ad-Blocker and Tracking/Privacy Protector.

Rated 4 out of 5 stars (496)
36,114 users

Stationery Requires Restart

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!

Rated 4 out of 5 stars (107)
35,580 users

GPO support For Firefox and Thunderbird

For work with new versions, use autoconfiguration module https://mozillagpo.sourceforge.io/
Firefox and Thunderbird extension to manage user preferences and user profile CA certificates using group policy

Rated 4 out of 5 stars (12)
33,896 users

CardBook Requires Restart Featured

A new Thunderbird address book based on the CardDAV and vCard standards.

Twitter: @CardBookAddon
Forum: https://cardbook.6660.eu/

Rated 4 out of 5 stars (167)
33,353 users