The 'Recently Bookmarked' list is really only a history, although, you can Delete bookmarks from there and they will also be deleted from your Library. It's much better to manage your bookmarks from the Bookmarks Library and they will be removed from the 'Recently Bookmarked' list.

Also, if you have inadvertently deleted bookmarks you can recover them by restoring a backup -

Restore bookmarks from backup

https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them

Thanks for this information but it doesn't solve my problem. I understand how 'Recently bookmarked' works but I still don't know how to delete the duplicate of my entire bookmarks without losing the original. See Printscreens - first showing beginning of Book mks and second showing beginning of duplicate copy. Nearly eighty, and not so technologically able, I need a step by step guide if you could provide that.

Managing bookmarks in the Bookmarks Library is not unlike working with files & folders in Windows Explorer. These articles should help you -

How do I delete a bookmark? https://support.mozilla.org/en-US/kb/how-do-i-delete-bookmark

Bookmarks in Firefox https://support.mozilla.org/en-US/kb/bookmarks-firefox#w_how-do-i-organize-my-bookmarks

Sort your bookmarks to quickly find the ones you want https://support.mozilla.org/en-US/kb/sort-bookmarks-quickly-find-ones-you-want

Use bookmark folders to organize your bookmarks https://support.mozilla.org/en-US/kb/bookmark-folders-organize-your-bookmarks ___________________________________________________________________

Restore bookmarks from backup https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them

"Recent" type folders are co called smart folders that show the result of a database query and what you see in the list aren't duplicates but are bookmarks stored elsewhere in a bookmarks folder. So do not get confused. Actions like a delete are done on the actual bookmark and as long as there are bookmarks left you will see items shown there (i.e, if you remove one then another takes its place).

In Firefox 96+ you can right-click a bookmark search/query result and click "Show in Folder" to locate this bookmark in the folder list.

You can use "Organize -> Undo" (Ctrl+Z) in the Bookmarks Manager (Library) to undo actions like an accidental (re)move done in the current session as long as you haven't closed Firefox.

Thanks for this guidance but it doesn't help. me to delete the duplicate copy. Following instructions for deleting more than one folder I am unable to select the duplicate copy as both copies are together in one folder. Under Toolbar and Other Bk Mks there are no folders, and under Bk Mks both the original and duplicate are together, one following the other. When I select and go to Organize and delete an entry, it still deletes from both the original and the duplicate.

If you are using an extension/add-on in regard to your bookmarks, you should disable it and restart Firefox. Leave the extension/add-on disabled and collapse the Recently Bookmarked folder, disregarding it until you have organized your bookmarks in the Bookmarks Library. After you are satisfied that duplicates have been removed in your other folders, expand the Recently Bookmarked folder and enable any relevant extensions.