Most Popular Extensions
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).
Send Later Requires Restart
True "Send Later" functionality to schedule the time for sending an email.
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!
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.
Mail Merge Requires Restart Featured
Mass Mail and Personal Mail
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.
Exif Viewer Requires Restart
Displays the Exif and IPTC data in local and remote JPEG images.
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).
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
Custom Buttons Requires Restart
Gives a possibility to create custom toolbarbuttons...
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.
ProfileSwitcher Requires Restart
It adds some options to launch easily other profiles and the Profile Manager.
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..."
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.
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...
Reinstates the extensions.checkCompatibility preference without respect to the current application version.
Copy Plain Text 2 Requires Restart
Copies text without formatting
Confirm-Address Requires Restart
Confirm E-mail address before sending mail
'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!