At one point several days ago I closed Thunderbird with two of my message folders open. Not whenever I open Thunderbird it opens with these same folders open, even though I may close it with no folders open or a message open or different folders open. Rebooting the computer did not solve the problem. This has happened twice. The first time I solved it by deleting the folder, but these are folder with a number of messages so I would rather solve the issue than use a workaround.