I was lucky to have a restore point to go back to, but afterwards I found that my original profile for Thunderbird was still intact. The profile contains emails, address books and other info.
I wonder if the "faulty" CCleaner update makes Thunderbird look in the wrong place for the profile? You can check where the profile is stored by going to "Help" in Thunderbird, then to "Troubleshooting Information". There you will see Profile Folder. If you click on Open Folder, you should see the location.
The path, in my case, is: This PC> Local Disc (C:)> Users> xxxx> roaming> Thunderbird.Profiles xxxx is your name
So if you find you have no account after the update, first check the path above. Then check the Troubleshooting information in Thunderbird to see if it points to the same place. If not, then move the profile to that location.
It's just an idea, not sure if it will work, but worth a try if you have lost your Thunderbird account and don't have a backup?
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