'''NOTE: Given the "in process" migration of this forum, this response may disappear later.''' Unfortunately, Microsoft has not provided a way to be able to synchronize back and forth your online Outlook.com/Hotmail with any other calendar. You '''can''' "publish" your Outlook.com calendar and have Lightning in Thunderbird subscribed to it. It will be read only in Thunderbird though. You will be able to see your calendar events, but not edit or change them. Or you can "publish" your Outlook.com calendar and save it as it is at the moment, to your computer, then import the calendar into Thunderbird. Then you will be able to edit and change the calendar, but the changes will not show up on your Outlook.com calendar. '''How to publish an Outlook.com calendar for use in Thunderbird:''' ''As of 2017-Feb-01'' 1. Go to your Outlook.com calendar in your web browser. 2. Click the gear icon in the top right of the webpage. 3. Select "Options". 4. Select "Publish calendar" under Options: Calendar: Shared calendars. 5. Select the calendar you want. 6. Under "Show availability, titles, and locations", click the "Create" Button. 7. You will see two links, one for HTML and one for ICS. You want the link for ICS. A. If you want to save the calendar to your computer, to import into Thunderbird, then right-click the link for the ICS file and choose "Save Link As", and save the file on your computer. B. If you want to subscribe to the Outlook.com calendar in Thunderbird (read only), then copy that link. '''Import the calendar to Thunderbird.''' 1. Go to the Calendar tab in Thunderbird. 2. Create a new calendar. Thunderbird menu: File: New: Calendar (If you cannot see the Thunderbird menu, press the Alt key or F10 key on your keyboard to show the menu) 3. Choose "On My Computer". Click "Next". 4. Name the calendar what you want and choose the color for the events that will be in the calendar. Click "Next", then "Finish". 5. Import the events from the saved file into the new calendar: Thunderbird menu: Events and Tasks: Import 6. Navigate to the ICS file you saved above, select it and click "Open". 7. Choose which calendar (your new one), to add the events to. Click "OK" '''Subscribe to the Outlook.com calendar.''' This will be read only in Thunderbird. 1. Create a new calendar. Thunderbird menu: File: New: Calendar (If you cannot see the Thunderbird menu, press the Alt key or F10 key on your keyboard to show the menu) 2. Choose "On the Network". Click "Next". 3. Select format "iCalendar (ICS)" 4. In the "Location" box, paste the link you copied in B above. 5. Select the option "Offline Support". 6. Click the "Next" button. 7. Name the calendar what you want and choose the color for the events that will be in the calendar. Click "Next", then "Finish".