Calendar and Date/Time
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.
Send Later Requires Restart
True "Send Later" functionality to schedule the time for sending an email.
Show Outlook Appointments (vcal / ics) Requires Restart
An extension to show embedded Outlook calendar (vcal / ics) parts.
Thunderbird doesn't show calendar parts from Outlook appointment emails. This addon adds a button to download the embedded appointment as ICS to import it into another calendar.
Add sync support for Exchange ActiveSync (EAS v2.5 & v14.0) accounts to TbSync
Open Google Calendar Requires Restart
Adds the Google Calendar web interface in a new Thunderbird tab. Creating and viewing events works like in a browser (Firefox, Chrome, ...)
TbSync is a central user interface to manage cloud accounts and synchronize their contact, task and calendar information with Thunderbird.
Purge Events Plus Requires Restart
Purge events from Sunbird and Lightning files and thereby cleanes the calendar
This extension adds support for CalDAV & CardDAV accounts to the Thunderbird Sync manager "TbSync".
NirvanaHQ Requires Restart
NirvanaHQ for Thunderbird
lightningWeather Requires Restart
LightningWeather shows the weather forecast in the background of the calendar so you can easily coordinate your activities with the weather.
Lightning Calendar Tabs Requires Restart
Displays tabs which allows quick navigation between time periods in Lightning calendar. All views of calendar are supported. Color of tab texts can be adjusted.
Todo.txt Requires Restart
Thunderbird extension for the Todo.txt application
Zonio Freebusy for Lightning Requires Restart
Finds when are people available for a meeting or event via Zonio Freebusy service. Displays freebusy blocks instantly in Invite Attendees window while attendees are being added. Works with both local calendar storage or any calendar provider.
More Snooze Requires Restart
This add allow to customize the snooze delay when snooze popup appears (lightning required).
Reply Monitor Requires Restart
**This is NOT COMPATIBLE with Thunderbird 31 or newer versions**
Keep track of your emails and replies (Lightning is required).
Note: the name of this add-on has been changed to Reply Monitor because the previous name is a registered trademark.
Events spanning multiple days Requires Restart
Displays multiple day events as a "spanning" event, without borders of the day-elements inside the month- and multiweek-view.
Gantt View Requires Restart
Gantt Chart view for Sunbird/Lightning
EDS Calendar Integration Requires Restart
Integrates calendars events with Gnome clock applet
Plugin may hang on Fedora.
As a workaround uninstall evolution-ews.
G-Hub Lite Requires Restart
Add Google Tabs to Thunderbird! Google services supported by G-Hub Lite: Calendar, Contacts, Drive, Docs, Sheets, Slides, Maps, Search, & Voice. Need G Suite / Google Apps? Check out G-Hub Pro: https://www.schiffner.com/index.php/software/g-hub-pro
Lightning Invitation Notifier Requires Restart
This extension is an extension to Mozilla Lightning for Thunderbird.
It shows a toast message and opens the invitations window when an invitation arrives.