Sync doesn't have a master file system, it just syncs in any direction. Unfortunately there isn't a way to undo it, it shouldn't have cleared your desktop bookmarks, though, just added your laptop ones to your current desktop. Did you lose your desktop bookmarks?

Firefox keeps backup in the bookmarkbackups folder, so you shouldn't have a problem with restoring an older backup.

• Bookmarks -> Show All Bookmarks -> Import & Backup -> Restore

The name of an automatically created JSON bookmarks backup in the bookmarkbackups folder includes a total item count (folders and separators included) and an hash value to prevent saving the same backup more than once. You also see this count in the Restore menu drop-down list.

• bookmarks-YYYY-MM-DD_<item count>_<hash>.jsonlz4.

See also:

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

THANK YOU, cor-el!

Yes, I noticed after my post that my desktop bookmarks were there, just scattered in between all the laptop bookmarks. It was a mess. I was able to do a restore okay per cor-el's instructions.