The starting point is to restart in troubleshoot mode (help menu) and continue when prompted to see if the folder really no longer exists or there is a problem with the addon.

Troubleshoot mode changed nothing. Actually there are 2 Junk folders.

1. 1 is here:

C:\Users\mark\AppData\Roaming\Thunderbird\TB Email Storage

1. 1 doesn't show up where it used to on the folders panel.
2. 2 here:

C:\Users\mark\AppData\Roaming\Thunderbird\Profiles\iyazvpry.default-release\Mail\Local Folders

1. 2 shows up in TB, but apparently isn't the"real" one that works. There is still no ability to junk an email.

.

I would expect the "real one" to be 2 as it located in what appears to the default location for a local folders "folder"

This "TB Email Storage" sounds like you have attempted to make some sort of customized location for Thunderbird to store mail. Even this URI: mailbox://markh%40marketfire.com@mail.marketfire.com/Junk looks like an IMAP account location perhaps post the more troubleshooting information from the help menu. Perhaps that will shed some light.

Well, I gave up and used brute force cybernetics. I restored all TB files from a 24 hour old backup - I do an incremental backup of the C: drive 2x a day, early and late. I have the pop server set to retain email for a few days. So a restore and restart put everything right, and all 2 day old mail was then downloaded. Once in a while a backup really pays off.....

The "real" Junk is located in TB Email Storage. Real, meaning I can junk an email, and filtering works. thx for your help.

Mark