Lightning Calendar keeps disappearing
Lightning calendar disappears after updates. Not sure if it just Thunderbird updates, Lightning updates or both but it disappears often and won't let me reinstall. Icon disappears. When I look in addons, it is not shown. When I try to add it, I get a message that will be enabled on restart. When I restart, I get the same message and it is not installed. Just gets stuck in this restart message loop.
I've tried as instructed in a number of posts to undo the uninstall, delete folders in profiles and nothing works. The only thing that seems to work is to delete calendar info, back up my profile using something like Mozbackup and reinstall Thunderbird. Gets time some.
Running Windows 7 and Thunderbird 38.3. Has been happening since early August 2015.
Thanks for any help.
Chosen solution
Don't know if this solved the problem but I survived an update from Lightning. First backed up everything with MozBackup. Completely uninstalled Thunderbird. Reinstalled thunderbird in safemode and restored profile. Survived update and keeping fingers crossed
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This is something of a strange issue, assuming it is truly going AWOL I am going to take the unusual step of asking you to send me your profiles.js file by email when the calendar is missing.
What I would ideally like is if you could take a copy as a backup while things are working. and a copy again when it has disappeared. The profiles.js file contains all your Thunderbird preferences, except your passwords.
To locate the file.
On the toolbar 
> Help> Troubleshooting information.
Click the show [profile button.
Close Thunderbird
backup the prefs.js file and open Thunderbird.
Now I assume it will take a couple of days at least to get two copies of the prefs.js file. Please email them to my address in the profile attached to my name here on the forum.with suitable attachment names that I know which is which. Please also link to this forum post as I really just loose them.
When the issue occurs, and have made copies, can you make sue Thunderbird is closed and replace the prefs.js file that has Lightning missing with the one you backed up while all was good.
Restart Thunderbird. Is the calendar back as it was?
Sorry I missed this response. It had worked for a bit but again, it is currently not working again. It went away when Thunderbird did a recent update. It went away. I got it back. Then Lightning did an update and it went away again. Could I do the opposite, and copy the profiles.js file while it is not working (now) and then get reinstall everything and send the one where it works again.
OK now I can add to the description of the problem. When Mozilla Firefox does an update the calendar disappears. Also now after a firefox update. It will not let me view my messages. I can only view the main screen for each account that has Email, Accounts and Advanced features on the screen. Do I have to scrap all things Mozilla?
Chosen Solution
Don't know if this solved the problem but I survived an update from Lightning. First backed up everything with MozBackup. Completely uninstalled Thunderbird. Reinstalled thunderbird in safemode and restored profile. Survived update and keeping fingers crossed