If this is something that has occurred recently it should be easy to sort out just unlink the device and revert to the previous version of bookmarks by using the restore option in the bookmarks library. With luck all you will loose is the last set of bookmarks added.

• How do I set up Sync on my computer?_remove-a-device-from-firefox-sync_2
• See Restore bookmarks from backup or move them to another computer

I always try to remind people using sync

• Sync only merges bookmarks now, it will not permit unidirectional syncing. For instance you cannot sync from a phone and just add those bookmarks to a computer, Sync will fill the phone with the desktop's bookmarks.
• It is wise to backup bookmarks manually if bookmarks are being synced.

My recommendation of caution and backing up of bookmarks is not aimed at those who inadvertently add a device. It is aimed at those who become over reliant on Sync. Occasionally; especially on slow connections or if there are many bookmarks changes; Sync throws a wobbly and corrupts or duplicates bookmarks. Without manual backups, these situations become almost impossible to sort out, by the time they are reported.

You can restore the bookmarks from the most recent JSON backup that was created before the Sync.

• https://support.mozilla.org/kb/restore-bookmarks-from-backup-or-move-them
• http://kb.mozillazine.org/Backing_up_and_restoring_bookmarks_-_Firefox

Thanks for the replies but that is not what I was asking. I already restored the bookmarks on my computers to the way I wanted them. What I am saying is that now there is content on the Firefox sync copy that I don't want coming down to my computers. I want to either remove that content from the sync copy or just remove the entire copy and start over.

If you want to delete the data stored on the Sync server then you can change the password of the Firefox account or delete the account and start anew with Sync.