Here's an old trick:

First, load one of the bookmarked pages from the missing folder into a tab.

Then click the blue star in the address bar to open the editing dialog.

Expand the folder list by clicking the v-like icon to the right of the folder name.

The current folder location should be highlighted in the hierarchy so you can see where it is.

Does that work?

If you have sync, and there is a problem anywhere, Shut Down Sync Immediately On All Devices to prevent the problem from spreading. Once the problem is fixed, perform the same repair on all computers/profiles before using sync again.

[v57+] Places Maintenance is built into Firefox.

Type about:support<enter> in the address bar.

You will find Places Database near the bottom. Press the Verify Integrity button.

When done, copy and post the results here.

the first solution did not seem to help. I tried to import an old backup. I found my missing folder in there. I now have a new problem. Is there a way to select multiple folders for deletion? I have approximately 100 redundant that I would like to delete.thanks in advance. Arvind

Open the Bookmarks Manager; Press the Alt or F10 key to bring up the toolbar, and select Bookmarks. Hot key is <Control> (Mac=<Command>) <Shift> B.

Select where you want to go using the 'tree' on the left. Or use the search box.

Make your first selection. Then, holding down the <shift> key, select others as well.

Warning ! ! Don't remove the entry you want to keep.

thank you very much. This was extremely helpful.

Glad to help. Safe Surfing.

Note that you can use "Organize -> Undo" (Ctrl+Z) in the Library to undo any changes made to the bookmarks in the current session (i.e. this won't work if you have close and restart Firefox).