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

You can check for issues with the places.sqlite and favicons.sqlite databases in the Firefox profile folder.

• use the "Places Database" -> "Verify Integrity" button on the "Help -> More 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 the most 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 an older bookmarks backup in the bookmarkbackups folder via the Bookmarks Manager (Library).

• Bookmarks -> Show All Bookmarks -> Import & Backup -> Restore
• 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 -> More Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> More 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

I had already tried the recommended .HTML Import and the Backup and Restore of the .json file from the bookmarks on the machine that I needed the bookmarks from and it didn't work. That's why I came here for support.

I shut down Firefox and deleted the places.sqlite and favicons.sqlite files as suggested. I tried to restore from the .json file after restarting Firefox and it did not work.

I decided to skip to the end and uninstalled Firefox and reinstalled it. I then tried to Restore from the .json file and now it complained that the file would not process is the wording I believe it used.

I went to my other machine to get a new copy in case the other was somehow corrupt but the problem was different since now I had an error message. I tried to Restore the fresh .json file and received the same error.

I still had the .HTML Export from the other day and Imported that successfully.

It is now working but I don't know what the original problem was.

Thank you for attempting to help me.