Note: I case it matters, my root email account is a POP account, not IMAP. About a week or two after this problem that I described above appeared, I noticed that the Junk folder (mailbox) had moved back to it's old position back under the root of my mail account without me doing anything deliberately to move it back. I assumed that its being moved to a position as a subfolder of Deleted must have been caused by a Thunderbird update which had then been reversed. I was happy, so I did not need to do anything more. But four months later, (which is now about a week ago, around April 23rd, 2019) I noticed that the Junk Folder was suddenly back under the Deleted Folder again, and I can't move it back to the Root of my mail account. What in the world is going on? Is the Junk folder being moved by updates to Thunderbird. If so that is a pain in the neck, and I'll have to live with it. Or am I doing something to inadvertently move it without noticing what I am doing? If I am moving the Junk folder accidentally, I can't figure out how I did it. And I can't reproduce the steps to move it back. If it is possible to move the Junk folder back to the Root of my mail account, can somebody, (anybody!) please tell me how to do it. Or if it is not possible please tell me that too so I don't go on trying to do the impossible.

Every folder "hangs" off of a parent. So it is just a matter of dragging it and dropping it on it's parent. The reverse of what you probably inadvertently did to get it where it is. Just drag the folder up the the michael walsh folder and drop it.

Matt, Perhaps you did not read what I wrote in the first part of my post.

I know how to move folders by dragging them, dragging is a trivial thing to do. I have been moving folders by dragging them for 20 years.

I wrote in my post that dragging DOES NOT WORK for the Junk folder. Other folders move easily by dragging but the problem that I described is that the Junk folder WILL NOT MOVE BY DRAGGING.

Thank you for attempting to solve my issue, but the solution you describe is not my issue.

I still have not found a solution to this problem so if there is somebody who does know the answer I would deeply appreciate any hints if you know that they DO WORK.

TRy this:

In Thunderbird Help > Troubleshooting Information Click on 'Open Folder' button

Exit Thunderbird now - this is important

click on 'Mail' folder click on 'pop mail account name' folder It will list your folders as mbox files - they have no extension. This is where the 'Junk' and 'Junk.msf' files should be located, but they may be missing. You will see a 'Trash.sbd' folder - click on folder to see contents. Move the 'Junk' mbox file out of the 'Trash.sbd' folder and put it up the directory so it is in the same location as the 'Inbox', Drafts', and 'Sent' mbox files. See image below as guide.

Delete the 'Trash.sbd' folder.

Restart Thunderbird.