Calendar and Date/Time
Montezooma Requires Restart
Montezooma is a Thunderbird Addon that adds zooming functionality to windows.
More Snooze Requires Restart
This add allow to customize the snooze delay when snooze popup appears (lightning required).
MultiBirthdaysReminder Requires Restart
This addon is now integrated into the new address book CardBook and thus it is no longer maintained
NirvanaHQ Requires Restart
NirvanaHQ for Thunderbird
The 'NoiaButtons' add-on offers cartoonish toolbar button icons (known from Noia themes) for default theme and lightweight themes. Further more lite silver and dark versions of Noia themes are included.
OBM Connector Requires Restart
OBM Lightning Calendar and addressbooks connector
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, ...)
This extension adds support for CalDAV & CardDAV accounts to the Thunderbird Sync manager "TbSync".
Add sync support for Exchange ActiveSync (EAS v2.5 & v14.0) accounts to TbSync
Purge Events Plus Requires Restart
Purge events from Sunbird and Lightning files and thereby cleanes the calendar
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.
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.
SanRockstar Requires Restart
Send Later Requires Restart
True "Send Later" functionality to schedule the time for sending an email.
Show Calendar Week Requires Restart
Shows the calendar week Thunderbird/Lightning calendar's moth and multi-week view.
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.
Simple Week View Requires Restart
A simple week view for Lightning, as in the print layout.
StormCows Requires Restart
Allows two-way access between Remember The Milk and calendar events or todo items.
Task Me (activity logger) Requires Restart
Activity logger (sampled task monitoring) which uses calendar to store user's activities.
It periodically displays window with textbox where user can put description of currently performed tasks. The description is saved in a calendar.
TbSync is a central user interface to manage cloud accounts and synchronize their contact, task and calendar information with Thunderbird.