Frequent bookmark-moving failures could point to a browser bug. Try updating or resetting the browser to fix it.

If you re-read my OP you'll see this has been the case for over a year on three macbooks with Firefox, multiple resets and always up to date.

TNT666, did you copy the same profile folder or profile files between computers? Or have you been using a particular add-on throughout the period that you have been having this trouble?

I am wondering whether this is a problem with your profile files or an add-on, rather than a bug in the Firefox software.

From my old to my temp macbook, everything was just transferred over, and it was a mess, a lot of libraries didn't transfer correctly (7 yrs difference between old macbook and temp), so on my new macbook M1, I reinstalled everything from scratch (a long and real pain too).

So are we saying this is a unique bug, that others have not experienced?

On my two older macbooks, my main problem was Firefox was constantly maxing out the cache memory and getting stuck/slowing down. This problem has disappeared with my M1.

I can still right-click to edit the bookmarks, it's just the double-click-drag that fails to move them. If this helps, when we "move" a bookmark there's a little indicator line that tells us where we are, akin to a cursor, but not. When the "move" fails, there's no indicator line, the bookmark gets selected, and opens instead.

TNT666, just to clarify, when you installed from scratch on the latest computer, did you completely abandon all your old user data, or did you transfer the previously existing bookmarks to the new computer somehow?

Of course I transferred bookmarks when all was said and done. However this is not an old bookmarks issue. It's happening to any and all new bookmarks.

TNT666, both old and new bookmarks are stored in the same database, so if a corrupted set of bookmarks was transferred then you might continue to see problems with both the original and newer bookmarks.

It might be worth checking the integrity of your places.sqlite file, which is where Firefox stores bookmarks.

To do this go to Help menu (press alt+H), select "More Troubleshooting Information", then scroll down to "Places Database" and press the "Verify Integrity" button.

If any errors are reported, try restarting Firefox and re-running the integrity check. You may want to try this again if errors are still found after the restart.

If no errors were found, or errors were found and fixed but the issue persists, then do you have similar problems if you right-click and choose cut and paste, rather than dragging and dropping the bookmarks? (I appreciate that your issue is one that may not always manifest, making such testing more difficult)

@techHorse there's a bazillion lines in that integrity report lots of "sane" What specific lines or key words am I looking for?

TNT666, sometimes people see lines that contain the term "error", for example "- The task queue was cleared by an error in another task." or "- Unable to check places.sqlite integrity: Error: Error(s) encountered during statement execution: database disk image is malformed".

Problem lines can also start with a "-", whereas non-problem lines can start with a "+", although I am not 100% sure off the top of my head if this is always the case. But lines starting with a "-" are something else to look out for.

Can you do a Cut and Paste in the Bookmarks Manager (Library) or in the bookmarks sidebar if dragging isn't working?

Right now my bookmarks are temporarily working fine. But ultimately, I'm not looking for yet more workarounds, I just want my bookmark-moving to stop failing. But apparently I'm the only one to have ever experienced this bug, and no one seems to understand why?