Are you possibly using Sync to sync bookmarks ?

If you use Sync then best is to disconnect Sync temporarily during troubleshooting.

This can be caused by a problem with the places.sqlite and favicons.sqlite databases in the Firefox profile folder.

• use "Verify Integrity" button on the "Help -> Troubleshooting Information" (about:support) page

If errors are reported with "Verify Integrity", close and restart Firefox or reboot and retry.

If "Verify Integrity" cannot repair places.sqlite, rename/remove all places.sqlite and favicons.sqlite files in the Firefox profile folder with Firefox closed. Firefox will rebuild places.sqlite and restore the bookmarks from a recent JSON backup in the bookmarkbackups folder.

• keep a backup copy of places.sqlite in case a new places.sqlite database has to be created

You lose the history when a new places.sqlite is created.

See also:

• https://support.mozilla.org/en-US/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file
• https://support.mozilla.org/en-US/kb/fix-bookmarks-and-history-will-not-be-functional

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

cor_el, First, I'm not syncing bookmarks, so that doesn't apply. I tried "Verify Integrity," and it worked for a while, but it stopped'. I tried "VI" again, but it didn't work. I copied and saved "places.sqlite" and then deleted both "places.sqlite" and "favicon.sqlite," but I still have the problem. What do I do now (besides leave the multiples alone)?

Restore Bookmark Backups

Firefox automatically makes backups of the bookmarks. These are stored in the bookmarkbackups folder.

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. Firefox 84+ <Control> (Mac=<Command>) <Shift> O.

Once the window is open, at the top of the page, press the button labeled Import and Backup. Select Restore. From the list, pick the file you want and click it.

The backups are stored in a jsonlz4 file named something like this; bookmarks-2016-06-29_1424_enD1GTH ya0JmicnYWg4V4g==.jsonlz4

In this example; 2016-06-29 = date created, 1424 = number of entries.

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

https://support.mozilla.org/en-US/kb/recover-lost-or-missing-bookmarks

https://support.mozilla.org/kb/forum-response-recover-bookmarks-after-update

If you remove places.sqlite then Firefox restores the bookmarks from the most recent backup. If this backup already has the duplicated bookmarks then you need to restore an older backup. You can check the item count for each backup to see if there is a backup with the expected number of bookmarks and restore this backup.

You can possibly use the tool to inspect a compressed backup.

• https://www.jeffersonscher.com/res/bookbackreader.html

cor_el and John McD, the reconstruction of "places.sqlite" returned me to my original state, but I still have the same problem. Apparently, when I bookmark a page, Firefox places two linked copies of my bookmark in my file, and when I delete one, the other goes with it. This leaves me with three questions:

       * Why does Firefox do this?
       * How do I prevent it from happening?
       * How do I correct the existing problem without losing any more entries?

Thanks.

If you are referring to the recently bookmarked list then this list shows the result of a database query, so all items you see in this folder are bookmarks stored in various bookmarks folders.

cor_el, I wasn't referring to the "Recently Bookmarked"--I was talking about the individual folders themselves. For example, I just went through my tags and found that I had 9 copies of the same entry, all with the same tags. That's what I'm dealing with--after all, I only need one copy in the bookmarks list.

cor_el, I apologize for not getting back to you sooner--I had (and still have, unfortunately) a bunch of computer-related problems to deal with. As for the duplicates, I found I can clear the duplicates from the individual folders, but cannot delete them from the "tag view" folders (the ones sorted by tags) . Is that normal, or do I still have a problem?

Thanks.

If you use Sync then best is to disconnect Sync temporarily during troubleshooting.

This can be caused by a problem with the places.sqlite and favicons.sqlite databases in the Firefox profile folder.

• use "Verify Integrity" button on the "Help -> Troubleshooting Information" (about:support) page

If errors are reported with "Verify Integrity", close and restart Firefox or reboot and retry.

If "Verify Integrity" cannot repair places.sqlite, rename/remove all places.sqlite and favicons.sqlite files in the Firefox profile folder with Firefox closed. Firefox will rebuild places.sqlite and restore the bookmarks from a recent JSON backup in the bookmarkbackups folder.

• keep a backup copy of places.sqlite in case a new places.sqlite database has to be created

You lose the history when a new places.sqlite is created. You may have to restore and older JSON backup in case the most recent version is already affected.

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

See also:

• https://support.mozilla.org/en-US/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file
• https://support.mozilla.org/en-US/kb/fix-bookmarks-and-history-will-not-be-functional

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

cor_el, I've already tried that (see above) and it didn't help. I don't see why it should work now.

If you want to remove one instance of a bookmark that has copies in another folders then you can remove the unwanted bookmark in the Bookmarks Sidebar or Bookmarks Manager (Library). If you do this via the "Edit This Bookmark" dialog (star button) then you remove all the copies.

cor_el, I can clear out the indexed folders. My problem is with the "tag folders," where I can't clear out the duplicates. Should I be concerned about this, and if so, what can I do about it?