There is another way, but best to go into Troubleshoot mode and see what happens there because it's also a test for other problems. If no problem in Troubleshoot mod, go to TB menu > Add-ons & Themes > Extensions tab. You can disable QuickFolders there.

Thank you. Going into Troubleshoot mode (with no QuickFolders operating) did not fix the problem. So here's the problem.

I had three messages in a folder. I wanted to move them to another folder. I forgot how to do that (how you must scroll through the complete list of folders to get to the target folder) so I accidentally dropped all three of the messages in the wrong folder. I was able to move two of the three messages to the correct folder, but the third will not budge. The interesting thing is that when I try to move it, it registers the target folder as if a successful move had occurred. You know, when I right click on the message, after the unsuccessful move, one of the choices is "Move to (name of folder) Again". And if I use that "again" option, the move doesn't occur.

So it moved the first time (as part of a group of three messages) but now it won't move. Any ideas?

Try R. click the folder that message is in > Properties > click 'Repair folder' button. Then try to move it again.

Thank you, that did it. I'm curious, is there a way to automatically repair all folders in Thunderbird with a single command?

Thank you, that did it. I'm curious, is there a way to automatically repair all folders in Thunderbird with a single command?

No, there is not. You could go into the profile and delete .msf files, but that's not something that typically needs to be done. Usually, it's only the Inbox that needs repair.