Lightning was discontinued when the Calendar was integrated into the base application in version 78 See https://www.thunderbird.net/en-US/thunderbird/78.0/releasenotes/

Perhaps read the user support article on calendars. https://support.mozilla.org/en-US/kb/creating-new-calendars.

The standard shortcut key to open the calendar tab is Alt+3

Thank you, Matt. I will work on this over the weekend.

Blessings to all!

Well, I guess I'm working on this now.

I opened the calendar tab now and previously, no problem. But the message at the top says:

>> All calendars are currently disabled. Enable an existing calendar or create a new one to create and edit events.

Of course, the message doesn't point toward HOW one might do these things. :) How might one enable the standard/default calendar?

Thank you!

Also, I am using an IMAP account connected to outlook.com (or whatever Microsoft is using for hotmail these days). If I enter a calendar event here, will it shop up in the calendar on our other computer, assuming that the same account is set up in Thunderbird on that machine?

Thank you.

I figured out how to enable the calendar (default, for now). My sync question remains, if anyone has a moment. Thank you.

Also, I am using an IMAP account connected to outlook.com (or whatever Microsoft is using for hotmail these days). If I enter a calendar event here, will it shop up in the calendar on our other computer, assuming that the same account is set up in Thunderbird on that machine? Thank you.

NO, because Outlook calendars use proprietary Microsoft technology and Thunderbird at this time only supports open standards. The standard carddav information interchange is not supported by Microsoft. There is a native exchange account type in the beta program and I would assume it will include contacts and calendars. Until then there is tbsync https://addons.thunderbird.net/en-us/thunderbird/addon/tbsync/ but you will need to also include the activsync module which it linked, but a separate download. It will sync you contacts