Here's the thing with Firefox Sync account login if there is nothing else besides that one computer connected to sync when you log back to sync that sync data check your current Firefox data and if there's nothing there it reset all those sync data thus wiping clean any data you had in sync. Mozilla/Firefox or Forum users can't help with your data retrieval here. What you should've done before this was use Firefox help on backing up your data/profile and bookmarks before doing what you did so you can restore them but as of what happened I doubt there anything to get back now.

Sync connects to a sync server and not device to device though.