There is no simple reversal of Sync. What you can do is roll back to an earlier version of Firefox by using the automated backups. That will lose any business bookmarks added since the date of the automated backup, and will only be possible if you synced recently and have an automated backup from before the Sync.

The automated backups display their date and number of bookmarks from User Interface in the the Bookmarks Library. It should be easy to see which backup contains Synced bookmarks because of the jump in the numbers. To Restore Use {Ctrl Shift B -Windows OR} Bookmark Icon (next to the star) -> Show All Bookmarks -> Import and Backup v -> Restore Select a suitable backup to restore from that listing. For full instructions see

• Restore bookmarks from backup or move them to another computer

I would strongly recommend making manual backups before first using Sync to sync bookmarks. I would also recommend making regular manual backups whilst Sync is in use for bookmarks.

• Restore bookmarks from backup or move them to another computer#w_manual-backup

At first thought it seems totally unnecessary to use sync and resort to backup bookmarks manually, after all the syncing effectively backs up bookmarks to multiple devices. The reasons for this counter intuitive suggestion are that Sync

• Now has only one option, merge. It will not do uni-directional syncs. It will attempt to make all bookmarks libraries identical.
• Sync is not totally reliable. Problems especially occur if there are slow internet connections and particularly if there many changes to bookmarks.
• Failure results in duplication &/or other corruption of the bookmarks libraries of the devices being synced. The task of sorting out the bookmarks after corruption is probably not feasible. All you can do is resort to whatever backups you have.

You can check for problems with the places.sqlite database file in the Firefox profile folder.

• http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox
• https://support.mozilla.org/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file

• Places Maintenance: https://addons.mozilla.org/firefox/addon/places-maintenance/

If you use Sync then best is to disconnect Sync (temporarily) while performing maintenance/repair efforts to the places.sqlite database.