Thank you for your help.

I tried emptying the inbox, deleting the 2 files, and restarting TB. I did the same for Sent and Trash.

I also deleted all .msf files for all inbox sub-folders and for all folders and sub-folders under "My Mail".

the problem persists.

My inbox has many sub-folders and sub-sub-folders should those be moved to My Mail?

Another problem I am having. I do not know if it is related. I have a stack of filters that move incoming mail into folders. The stack ends with 2 filters.

(1) a filter that checks whether FROM is from someone in my mail lists. It then moves the message into a folder called "Known Sender".

(2) a psuedo-ELSE filter that check whether the subject contains a very improbable string. It put the message in a folder called ") Suspicious". Sometimes I still end up with folders in Inbox that clearly should be in the two folders, "Known Sender" or ") Suspicious".

Do you mean I should remove all sub-folders and all sub-sub-folders from inbox?

Should I move messages from Inbox folders, sub-folders and sub-sub-folders to "My Mail" or would it be better to move them to local folders?

Thank you. I'll move all my inbox folders, sub-folders, and sub-sub-folders from My Mail to Local folders.

Should I move all my other My Mail Folders to Local folders or only the ones that are sub parts of inbox?

WRT backup, I run Mozbackup and also copy the .default file to desktop before I do any of the attempts to fix these problems.

How do I know which folders need repair?

3 times I have: moved all messages out of the inbox itself into sub-folder, sub-sub folders, and other folers, etc. under My mail. run mozbackup copied the profile (.default) to the desktop deleted inbox and inbox.msf from the profile

the problem persists.

Thank you for your frequent replies.

I only have the Microsoft Defender. I'll turn it off for a while. During that time I'll not use Firefox or anything else that connects to the internet. I'll try TB a couple of times. It is almost 5pm and a lot of mail should come in the next couple of hours.

I still received the message with 1969 dates.

I do not know if this may be causing some of the problems. MozBackup produces the message in the attached clip about unknown files. Are these files I should remove from the profile?

I am about to create a new profile again.

Since your advice I created a new profile twice. Also all my messages that I need to keep are now in Local Folders. Messages remain i Inbox only until I delete them or move them on a local folder.

What I hope is my last point to clarify is: Can a message folder (one with no filename extension aka file type) still carry corruption? Do I need to move folders a few at a time and then wait until I use TB to see if problems remain?