If you haven't closed out of Firefox since this happened, and you wouldn't lose too many other changes, you could try this in the Library dialog:

(menu bar) Organize > Undo

Next suggestions:

(1) Export your bookmarks to an HTML format file, open the HTML format file as a web page in Firefox (in a tab) and then use Find (Ctrl+f) within the page to discover the current location of the folder. This is a convenient reference format, and also a kind of backup, but of course it's static and won't update in real time.

See: Export Firefox bookmarks to an HTML file to back up or transfer bookmarks

(2) Install the Show Parent Folder extension, choose its option to show the whole path, and add that column to the Library dialog's bookmarks list.

See: https://addons.mozilla.org/firefox/addon/show-parent-folder/

I haven't used this extension for a while, so I don't recall the details about how it works.

If you have found the bookmark via a search, but do not know what folder it is in then you can open this bookmark in a tab. You can open the bookmark in Offline mode (File > Work Offline) to prevent opening the link from internet. You can click the blue highlighted star to open the "Edit This Bookmark" dialog. The "Edit This bookmark" dialog shows details (properties) including in what folder the bookmark is located. You can open the full folder tree via the Down arrow button that is positioned outside the folder field and scroll down (drag the scroll thumb or use the mouse scroll wheel) until you see the selected folder.

cor-el, I tried but all that does is show all the bookmarks, no full folder tree. Let me explain my problem better.

I had a folder "General", which had 4 sub-folders. (In Library, I can search and find a few files, but that doesn't show folders.) Seems as if "General" folder has to be somewhere, so I'd like to find it and have it display in my Bookmarks menu that I always keep open when navigating the web.

Oh, FF, if only you made life easier in this situation. I'd think the Techies accidentally do this, too, and would welcome an easy way to find it. sigh.

pizazz

jscher, it worked! I wasn't sure about the "Undo, as I was in Library and all it did is bring me up 1 level. But then I did the export to HTML file and did a "Find", and there it was. (I almost couldn't find the html file. I gave it a name, bub didn't find it in documents folder. finally did a search of my C drive and it appeared. whew!)

I'm going to write this down as I know I'll need it again, lots of times. wow, I'd never have known how to find my misplaced folder. FF needs to be more user friendly when it comes to something like this. it should be a snap. instead, i rack my brain trying everything I can think of.

thank you for the solution. pizazz