This sometimes happens when Thunderbird is updated. Other software (antivirus? VPN?) interrupts the process, causing thunderbird's update of the prefs.js file to fail. When this happens, the updates appear in prefs-1.js. On a restart, Thunderbird starts fresh, causing you to reenter email info. exiting thunderbird, locating the prefs-1.js and renaming to prefs.js generally restores everything.

Hello David,

Thank you for your response. I have been able to use your information to apparently solve my problem. But in my case, I actually had seven prefs.js files, the original plus numbers 1 through 6. So instead of renaming prefs-1.js, I renamed prefs-6.js because it seemed like the newest file from the bunch.

I think that this has solved the problem. We'll see in the days and weeks ahead.

Thank you for your intervention and advice!

You're welcome. :)