You might look at the following extension.

https://addons.mozilla.org/en-US/firefox/addon/default-bookmark-folder/

That "Show editor when saving" checkbox should still be there.

The "Edit This Bookmark" dialog that opens if you click the highlighted star has a checkbox with "Show editor when saving" (shortcut key in the dialog is Alt+S). This item is at the bottom just above "Remove Bookmark" and "Done". You can click the highlighted star a second time to open the "Edit This Bookmark" dialog.

See "How do I change the name or location of a bookmark?"

• https://support.mozilla.org/en-US/kb/bookmarks-firefox

You can check this pref on the about:config page and make sure it is true.

• about:config => browser.bookmarks.editDialog.showForNewBookmarks = true
• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or userChrome.css is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Thanks, the about:config method did the trick. Probably one of my privacy extensions is interfering with regular operation (Alt-S doesn't work either; when I press it, the proper dialog doesn't appear; instead, it opens History). But now the Edit Bookmark dialog does appear when I initially create a bookmark, which was the immediate goal.

I haven't checked with Troubleshoot mode, as this solves my immediate problem. I'll keep the Troubleshoot mode in mind, though. Thanks very much.