In all probability you need to fix your antivirus product of choice, or allow Thunderbird to shut down before you disconnect the power. Thunderbird saves settings on exit. If some antivirus product is messing about scanning the files i is trying to write then the save fails and the settings revert to default on the next startup. Then we get people here complaining that their settings changes are not saved. If you think it is frustrating, image where we are sitting, trying to tell people that the product they see failing is not where the problem is. It is always possible that there might be a bug, but there are so many problems with antivirus products, streaming backups, cloud storage attempts etc that if such a bug exists it is lost in all the noise from third party products.