Lightning Featured

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.

Rated 3 out of 5 stars (1,875)
5,386,765 users

Session Manager No Restart

Session Manager saves and restores the state of all or some windows - either when you want it or automatically at startup and after crashes. It can also automatically save the state of open windows individually.

Rated 4 out of 5 stars (568)
283,041 users

µBlock No Restart

Finally, an efficient blocker. Easy on CPU and memory.

Rated 4 out of 5 stars (212)
222,138 users


A clean, easy to use and highly extensible Internet Relay Chat (IRC) client.

Rated 4 out of 5 stars (126)
149,257 users

UnMHT No Restart

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 5 out of 5 stars (217)
84,321 users

FoxClocks No Restart

FoxClocks shows times around the world - or just your local time - at the bottom of your browser. It deals with daylight saving time so you don't have to.

Rated 4 out of 5 stars (311)
66,739 users


Synchronizes contacts & groups between Thunderbird or SeaMonkey and Google Contacts. Imports Facebook friends, contacts you follow on Twitter, and more.

Rated 4 out of 5 stars (202)
65,296 users

Send Later

True "Send Later" functionality to schedule the time for sending an email.

Rated 5 out of 5 stars (39)
56,004 users

Copy Plain Text 2

Copies text without formatting

Rated 5 out of 5 stars (62)
39,764 users

Mail Redirect

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

Rated 4 out of 5 stars (124)
33,073 users

Copy As Plain Text

Removes formatting from copied text.

Rated 4 out of 5 stars (56)
26,279 users


A simple note-taking extension.

Rated 5 out of 5 stars (169)
26,026 users

Snap Links Plus

Select a number of links with a rectangle and open them all in new tabs in the same or a new window(s), download them or copy them to the clipboard. You can also lasso checkboxes to quickly check or uncheck them.

Rated 4 out of 5 stars (97)
22,792 users

Filter Uploader for Adblock Plus

DOES NOT BLOCK ADS! Don't install this add-on if you don't know what 'uploading' means!

This add-on Uploads the filters from your Adblock Plus installation to a FTP, HTTP, HTTPS server...

Rated 3 out of 5 stars (45)
22,275 users


Persistent sticky notes for Thunderbird associated to mails.
This is a port to Thunderbird >= 3 and Seamonkey >= 2 based on XNote 2.1.0 ( https://addons.mozilla.org/en-US/thunderbird/addon/3093 ) with bugfixes and additional features.

Rated 5 out of 5 stars (64)
19,103 users

AutoCopy 2

Copies selected text to the clipboard automatically.

Rated 5 out of 5 stars (57)
18,604 users


SmartTemplate4 offers an easy way to automatically create customized replies by auto-inserting various mail headers. Templates can be created for every account as well as for the default (all email accounts). Also supports the Stationery Add-on.

Rated 5 out of 5 stars (49)
17,338 users

MinimizeToTray Plus

Note from Mozilla: This add-on has been discontinued. Try MinimizeToTray Revived instead.

Minimize applications to the system tray.

Rated 4 out of 5 stars (193)
17,012 users

Add-on Update Checker

Adds Tools menu item to check Add-ons for updates. Includes toolbar icon.

Rated 4 out of 5 stars (51)
14,549 users

Quote Colors

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.

Rated 4 out of 5 stars (43)
13,515 users