Tech Q -- Thunderbird Lost Local Folders

A bunch of my local folders got zapped. I think it was when installed v. 13 last week. I didn’t immediately notice because they are ones I archive items to, and I don’t display the full list when I am not using that group of folders.

I can’t find the missing stuff in my back-ups. The successive versions of Eudora and Thunderbird seem to have mailboxes stashed all over the place, and I either missed backing up the right place, or the back-ups are under some name I don’t recognize as associated with Thunderbird.

Searches of the Mozilla/Thunderbird forums and knowledge base, and of the 'net in general, didn’t turn up anything particular to the last few releases of Thunderbird.

What did turn up was advice for fixing this problem in practically every freakin’ previous release. So I seem to have dodged a lot of bullets.

Does anyone have any idea how I might recover from Thunderbird 13’s version of this hardy perennial?

I run 64-bit Windows 7, Avast & Comodo, keep everything up-to-date.