It may be lagging while talking to the server. I find that reordering folders is very fast with Local Folders and sluggish with IMAP folders. But I don't recall it ever not working at all, I just sometimes have to be a little patient while things get in gear.

I kind of hate the folder ordering procedure. It's too fiddly and prone to error and more than once I've dropped a folder into another by accident, which can take a long time to recover from if it's a large IMAP folder.

This may or may not be helpful, but I discovered this recently: when you grab a folder, move it over to the right a bit, then move it between two adjacent folders, I see a tiny dot, just a pixel or so, which is the indicator that I can now drop it between them. If I see an adjacent folder surrounded by a box, it will go into that folder when I drop it. I don't see a "blue placement line" but that might be because of my color choices.

Thanks for the helpful reply but it doesn't work for me :(

When I drag and try to place a folder I get a blue line showing if / where a folder can be placed. I have just tried to do this with the default 'Archives' folder and the blue line only shows when the dragged file is hovering in certain places. What is going on???

I've just done a search for 'when can folders be dragged in thunderbird' hoping to find something definitive on the rules for this procedure. Some results seem to suggest this can't be done and that to do so requires the use of parent / child folders.

What is the intended default behaviour for dragging and dropping of folders (for both default folders like 'Inbox' and user created folders)? Should I be able to do this or not? This shouldn't be so complicated...

What version of Thunderbird?

What is your operating system?

Please provide a screen shot showing the "blue line".

The add-on "Manually sort folders" used to be needed to reorder folders. Eventually that feature became built into a more recent version of Thunderbird, 140.x, I think.