Multimonth view

Multimonth View allows users to display multiple months in a single calendar view,

CalendarSearchExport

Exports the results of a search in calendars

Date Time Formatter

Shows relative date-time in the column.
Note: you need to click "Select columns to display" and then -> "Relative Date/Time"

All Events

Define your own time ranges for appointment searches

ElsHelp

Extension for ElSchool diary

iCanban - Kanban with ICAL

Allday Tasks

Thunderbird lacks the ability to create and manage allday tasks. This add-on adds these capabilities.

Message Links 4 events

Allows to use links to messages in the description field of events and task

Calendar/Project Tools: Gantt-/Year View, Planner

*Display Gantt View and Year View
*Task Time Planning: daily, distribute your open tasks into open time slots.
*Show parent/child relationships for tasks

Outlook Calendar - Quick Access

This extension adds a simple button to your Spaces toolbar that opens in a new tab, providing you with one-click access to Outlook Calendar.

Create Calendar events from mail content

This plugin offers to create new events based on the email subject and content

Outlook/Teams Appointments

Get the hidden appointment from an email from outlook/teams as a .ics-file - Icon: https://fontawesome.com/

Birthday Calendar

Adds calendars containing the birthdays from your address books.

Date detection

Turn the dates and time references in your email (e.g. "tomorrow", "in 2 hour") into clickable links. Clicking them will create an event at the corresponding date.

Mahoor-Iranian-Date

This add-on adds a new column called "Persian Date" in recent versions in message list containing Iranian Date.

It is reimplementation of Iranian date for Thunderbird 78+ and 115+. The source is based on Full address column by Łukasz Kosson.

GCalTab

GCalTab is a Thunderbird add-on that opens Google Calendar website in a Thunderbird tab. It features a beautiful dark mode thanks to the DarkReader algorithm.

Iranian Date For Thunderbird Requires Restart

Adds a new Iranian(Persian/Jalali) date column to Thunderbird.

Google Calendar Tab

Adds a button to open Google Calendar in a new Tab

marked-lightning

Extension for Lightning: Allows the use of Markdown in Task descriptions and renders them as HTML in the TaskView.

M-Hub Lite

Add Microsoft Office 365 Tabs to Thunderbird! Services supported by M-Hub Lite: Calendar, People, OneDrive, Word, Excel, PowerPoint, & Bing. Need business or enterprise support? Get M-Hub Pro: https://www.schiffner.com/software/m-hub-pro