I have been a loyal Thunderbird user for many years now and have never had a problem until I upgraded to Windows 8.1 My problem has happened twice: For no known reason, all of a sudden all of my messages (including the actual subfolders) disappear. I have checked the trash - not there. I have even looked at the folder on my drive that contains my profile information, and all of the subfolders have even disappeared under the Mail folder. This is really upsetting and confusing. Is this happening because there is some incompatibility issue with the latest automatic upgrades to Thunderbird and Windows 8.1, or must there be something that I am doing in the new Windows 8.1 OS that I am unaware of? I either have to solve this problem or switch to another email client (which I desperately don't want to have to do). It is just not feasible for me to suddenly lost all of my mail that I have saved for future reference.