Essentially, the user is unable to "view" the moving/deleting/sorting of bookmarks, after an initial change. So, you can take one action (moving/deleting/sorting), after which, the bookmark window appears to freeze, until you close it and reopen it. It will not scroll, it does not appear to let you edit bookmarks--everything is frozen, like a screenshot.
This occurs in both the Sidebar and the Show All Bookmarks Window.
This occurs in Safe Mode and Full Mode.
This occurs after exporting all bookmarks to another browser (Chrome/Safari/etc.) and reimporting.
This occurs with Extension On or Off.
I have followed all troubleshooting processes documented on support.mozilla.org.
I am running the latest update for Firefox.
This existed several years ago (I do no recall when--at that time, I just lived with it) and it eventually resolved itself with an app update (I do not know which one, or why). The most recent Firefox update reintroduces this issue.
I suspect it has something to do with how the bookmark file refreshes/renders to the window after an edit or state change is made.
I often recommend turning on telemetry, it was brought out after developers failed to spot regressions and gives them insight into real world performance of Firefox. It will pick up some of the problems with hangs in bookmark use. Once it has been running you may of course see the data yourself.