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

You can check for problems with the places.sqlite database (bookmarks and history) in the Firefox profile folder.

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

See also:

• http://kb.mozillazine.org/Locked_or_damaged_places.sqlite
• https://support.mozilla.org/en-US/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file

If "Verify Integrity" on the "Help -> Troubleshooting Information" (about:support) page cannot repair places.sqlite then remove all places.sqlite files in the Firefox profile folder. 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
• http://kb.mozillazine.org/Unable_to_process_the_backup_file_-_Firefox

You may have to restore an older backup in case the recent backup is corrupted.

• Bookmarks -> Show All Bookmarks -> Import & Backup -> Restore
• https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them

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 Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Hi, if you install over top or uninstall and install some folders get duplicated like Bookmarks Toolbar

I deleted all of my bookmarks before restoring a prior set from my saved bookmarks. All was well. All was still well before I went out for dinner this evening. When I came home, I had a significant number of duplicated bookmarks in several of my folders (not all of them, just some). I also had another set of the same folders to the right side of my regular set. I did not restore any additional bookmarks before this happened. I have, again, deleted all of my current bookmarks and restored a previous set. We'll see how long this lasts.

In addition to the information above, I DO NOT USE SYNC. I don't know what bookmarks are synced to what, but the bookmarks that are on my computer after the sync bear little similarity to the bookmarks I use and are not any set of bookmarks I have EVER set up or used. I won't use sync any more for that reason.

(I tried deleting this, but it won't let me.)