You need to upgrade lightning to match the new version. Every version of Thunderbird has a matching version of Lightning. Upgrade Lightning and all your events will fill back in. Next time do not skip the step to check for add on upgrades.

Lightning 2.6.6 was for Thunderbird 24.x

Lightning 3.3.1 is for Thunderbird 31

https://addons.mozilla.org/en-US/thunderbird/addon/lightning/versions/

I tried this but after I downloaded 3.3.1 and tried to save it a message came up saying This file does not have a program associated with it for performing this action. Create an association in the Set Associations control panel. I'm not very computer-literate - how do I do this and will it work anyway? I'm using Thunderbird 31.3.0.

Sorry - this may be sent twice!

Download the file to someplace that you can find it like the Desktop.

Then in Thunderbird go to the Add on page either from the menu bar using Tools-Add ons or using the AppMenu button then Add ons.

On the top of the add ons page is an icon that looks like a gear. Click that and select Install Add On from File.

donferg said

thunderbird 31.3.0 Lightening 2.6.6 - shows disabled on 'extensions' How can you upgrade without the extensions/add-ons being ready? How do I get my calendar back?

Worked like a charm for me. Thanks much

Thank you! It worked and my calendar is now back. Very, very easy to do with your simple and clear instructions. I downloaded it to Documents by the way.

All is well - calendar back