This usually means something is interferring with Thunderbird's update of settings at shutdown. This might be an antivirus product or other firewall issue. This can often be verified by clicking help>troubleshootinginformation, scroll to 'profile folder' and click 'open folder.' the settings file is named prefs.js. If you see more than one, such as prefs-1.js, prefs-2.js, that is an indication of the problem. This occasionally happens when prefs.js is marked read-only. I do not know the solution for your particular situation. Let me know results of your review.

So I checked that directory. There are prefs-1.js through prefs-18.js. So your suspicion was correct. Now to figure out the solution.

To fix the immediate issue, try this: - exit thunderbird - delete all of those except the highest-numbered one. - rename that one to prefs.js - that will contain your last attempted update. - if the attempt to delete the original prefs.js says it doesn't exist, you may need to unhide it.

This doesn't solve the issue, but may at least restore your intended setting. my first suspicion would be theantivirus. see you can tell it to avoid the appdata\roaming\thunderbird folder.

You're right. When I tried to rename the most recent one, it wouldn't let me saying there's an existing file of that name. However I can't seem to unhide it. I tried properties on the directory but it's already set to show hidden files.