open the troubleshooting information on the help menu. Click the show profile button Close Thunderbird Open the "mail" folder in the file manager window that opened. Delete the folder names "smart mailboxes" Restart Thunderbird.

What was the problem with version 115?

Unable to do as suggested. No "troubleshooting information" menu, but there is "More troubleshooting information" so clicked on that, resulting in a page headed "Troubleshooting information". No "show profile" button visible, though. Under "Application basics" there is an entry for "Profiles", which gives a link to "about:profiles". This leads to the addresses of the Root directory and the Local one, and the option to restart normally or with add-ons disabled. What should my next step be? Would appreciate any help.

Open the "mail" folder in the file manager window that opened. Delete the folder named "smart mailboxes"

A postscript to my earlier reply, as it seems I did not specify the problem correctly. What had happened was that on going to 102.15.1 no foiders were displayed. Eventually, the answer was found here:

https://support.mozilla.org/en-US/kb/switching-folder-pane-view

"Select View > Folders from the menu bar, or select Folders from the application menu, to choose the view you want to use."

I went from the menu bar's View > Folders > All, which did the trick. Obvious, once you know (like so much else).