Most Popular Extensions

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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 (151)
68,093 users

Send Later Requires Restart

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

Rated 5 out of 5 stars (84)
67,169 users

Forecastfox (fix version) Requires Restart

Get international weather forecasts from AccuWeather.com and display them in any toolbar or statusbar with this highly customizable and unobtrusive extension.

Now Available for: Firefox, Thunderbird and SeaMonkey!

Rated 5 out of 5 stars (231)
65,822 users

KeeFox Requires Restart

Simple and secure password management. Login automatically, never forget another password, stay in control of your passwords and improve their security. Powered by the world-renowned KeePass Password Safe.

Rated 5 out of 5 stars (1,317)
64,417 users

Mail Merge Requires Restart Featured

Mass Mail and Personal Mail

Rated 5 out of 5 stars (147)
59,841 users

FoxClocks

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 (330)
58,686 users

Exif Viewer Requires Restart

Displays the Exif and IPTC data in local and remote JPEG images.

Rated 4 out of 5 stars (87)
57,405 users

Thunderbird Conversations

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).

Rated 4 out of 5 stars (437)
57,086 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 (85)
56,023 users

Custom Buttons Requires Restart

Gives a possibility to create custom toolbarbuttons...

Rated 4 out of 5 stars (124)
55,288 users

Google Docs Viewer (PDF, DOCX, PPTX, XLSX, etc...) Requires Restart

View publicly-accessible PDF, DOCX, PPTX, XLSX, among other files online with Google Docs by only 2 clicks. Click as usual for your default viewer. Support bookmarked URLs. Security and your explicit viewing intention are always honored.

Rated 4 out of 5 stars (64)
53,618 users

ProfileSwitcher Requires Restart

It adds some options to launch easily other profiles and the Profile Manager.

Rated 4 out of 5 stars (96)
49,289 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 (139)
48,199 users

Ad-Blocker

Ad Blocker lets you block all ads, tracking & malware from the web world. It is an effective solution to browse the web without offensive and annoying ads you hate to see.

Rated 4 out of 5 stars (21)
43,943 users

rikaichan Requires Restart

Japanese to English/German/French/Russian dictionary. Just hover the mouse on top of a word, and a popup appears. Automatically de-inflects verbs and adjectives. Detailed kanji view...

Rated 5 out of 5 stars (108)
42,648 users

Disable Add-on Compatibility Checks

Reinstates the extensions.checkCompatibility preference without respect to the current application version.

Rated 4 out of 5 stars (108)
42,204 users

Clean Links

Converts obfuscated or nested links to genuine clean links.

Eg: http://somesite.com/?to=www.example.comhttp://www.example.com/

Rated 5 out of 5 stars (126)
42,165 users

Copy Plain Text 2 Requires Restart

Copies text without formatting

Rated 5 out of 5 stars (82)
41,797 users

Confirm-Address Requires Restart

Confirm E-mail address before sending mail

Rated 4 out of 5 stars (33)
41,432 users

Classic Toolbar Buttons

'Classic Toolbar Buttons' add-on restores old toolbar button ui (known from Fx 4-7s small view, Fx 4-12s large view & Tb 5-14) for current Firefox, Thunderbird and Seamonkey versions.

Beta builds on versions page!

Rated 5 out of 5 stars (163)
38,026 users