Requires you to find your profile folder and delete stuff, I got mine back by first deleting global-messages-db <- this is a file Then going into the Mail folder and deleting smart mailboxes <- this is a folder Note, exit thunderopps and when you restart, you get back a sort of view, I'm ticked now because all my custom folder layouts are gone. PROFILE: C:\Users\[username]\AppData\Roaming\Thunderbird\Profiles\[funnystring].default Note: AppData is hidden, you can get to it just by clicking in the address bar of windows explorer and typing it in there.