I may be able to help you. I encountered this exact same problem on an older Windows 7 computer that has historically had difficulty keeping Lightning (i.e., the Calendar) during Thunderbird upgrades. Often, Lightning would appear disabled pending a restart in Add-Ins. When that happened, I had to exit Thunderbird, point Windows Explorer to %userprofile%\AppData\Roaming\Thunderbird\Profiles\xxxxxxxx.default\extensions (substitute your 8-character profile ID for the "xxxxxxxx") and manually copy the new calendar files out of the Staging folder.

After upgrading to Thunderbird 60.3.0, my calendar disappeared, and Lightning appeared in the Add-Ins list as being incompatible with Thunderbird 60.3.0. Like you, I followed the troubleshooting steps and got nowhere. After a lot of fruitless searches, I decided to try the upgrade on my Windows 10 laptop, which has never had problems with a Thunderbird upgrade. Sure enough, it performed the upgrade flawlessly, so I then went to look at my %userprofile%\AppData\Roaming\Thunderbird\Profiles\xxxxxxxx.default\extensions folder and see what looked different. Much to my surprise, on my Windows 10 laptop, there was no subfolder for Lightning. Aha, so the new version stores calendar data elsewhere. So, I tried renaming the Lightning subfolder on my troublesome Windows 7 computer, and voila, the calendar came back, all nicely upgraded for Thunderbird 60.3.0!

So, to fix your problem, try this:

1. Exit Thunderbird.

2. Point File Explorer (Windows 8 and newer) or Windows Explorer (Windows 7 and older) to %userprofile%\AppData\Roaming\Thunderbird\Profiles\xxxxxxxx.default\extensions. Again, substitute your 8-character profile ID for the xxxxxxxx.

3. Look for a folder named {e2fda1a4-762b-4020-b5ad-a41df1933103}. If you find one, rename it. (I renamed mine to "delete {e2fda1a4-762b-4020-b5ad-a41df1933103}".)

4. Restart Thunderbird.

I hope this helps you!

I forgot to mention: If renaming the folder fixes the problem, you can safely delete the renamed folder later.

lebowitzit said

I may be able to help you. I encountered this exact same problem on an older Windows 7 computer that has historically had difficulty keeping Lightning (i.e., the Calendar) during Thunderbird upgrades. Often, Lightning would appear disabled pending a restart in Add-Ins. When that happened, I had to exit Thunderbird, point Windows Explorer to %userprofile%\AppData\Roaming\Thunderbird\Profiles\xxxxxxxx.default\extensions (substitute your 8-character profile ID for the "xxxxxxxx") and manually copy the new calendar files out of the Staging folder. After upgrading to Thunderbird 60.3.0, my calendar disappeared, and Lightning appeared in the Add-Ins list as being incompatible with Thunderbird 60.3.0. Like you, I followed the troubleshooting steps and got nowhere. After a lot of fruitless searches, I decided to try the upgrade on my Windows 10 laptop, which has never had problems with a Thunderbird upgrade. Sure enough, it performed the upgrade flawlessly, so I then went to look at my %userprofile%\AppData\Roaming\Thunderbird\Profiles\xxxxxxxx.default\extensions folder and see what looked different. Much to my surprise, on my Windows 10 laptop, there was no subfolder for Lightning. Aha, so the new version stores calendar data elsewhere. So, I tried renaming the Lightning subfolder on my troublesome Windows 7 computer, and voila, the calendar came back, all nicely upgraded for Thunderbird 60.3.0! So, to fix your problem, try this: 1. Exit Thunderbird. 2. Point File Explorer (Windows 8 and newer) or Windows Explorer (Windows 7 and older) to %userprofile%\AppData\Roaming\Thunderbird\Profiles\xxxxxxxx.default\extensions. Again, substitute your 8-character profile ID for the xxxxxxxx. 3. Look for a folder named {e2fda1a4-762b-4020-b5ad-a41df1933103}. If you find one, rename it. (I renamed mine to "delete {e2fda1a4-762b-4020-b5ad-a41df1933103}".) 4. Restart Thunderbird. I hope this helps you!

Thank you, thank you, THANK YOU. . . .it worked!!!

It took a little time, but I was able to find everything & it WORKED!!! Wonderful, cannot thank you enough!