Calendar and Date/Time
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.
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.
MultiBirthdaysReminder Requires Restart
This addon is now integrated into the new address book CardBook : https://addons.mozilla.org/thunderbird/addon/cardbook/ (and thus it is no longer maintained)
More Snooze Requires Restart
This add allow to customize the snooze delay when snooze popup appears (lightning required).
SanRockstar Requires Restart
Reply Monitor Requires Restart
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.
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.
MiniWebView Sidebar Requires Restart
Sidebar that shows a single web page. This allows Thunderbird to be augmented with any user-supplied or third-party web page. The screenshot shows an example - I use my own custom web page to present my Google Calendar in my preferred format.
StormCows Requires Restart
Allows two-way access between Remember The Milk and calendar events or todo items.
Todo.txt Extension Requires Restart
Thunderbird extension for the Todo.txt application
EDS Calendar Integration Requires Restart
Integrates calendars events with Gnome clock applet
Plugin may hang on Fedora.
As a workaround uninstall evolution-ews.
Purge Events Plus Requires Restart
Purge events from Sunbird and Lightning files and thereby cleanes the calendar
Lightning Requires Restart 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.
G-Hub Lite Requires Restart
Add Google Tabs to Thunderbird! Services supported: Voice, Calendar, Drive, Docs, Sheets, Slides, Hangouts, Plus, Photos, Contacts, News, Maps, & many more. Need Google Apps? Check out G-Hub Pro: http://www.schiffner.com/index.php/software/g-hub-pro
Montezooma Requires Restart
Montezooma is a Thunderbird Addon that adds zooming functionality to windows.
Macro Template is to replace mail templates with macros for date formatting.
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.
Lightning Colors Reminder Requires Restart
Let's show the calendar color on Lightning reminders!