Firefox on PC - sync issues

Hi I have 2 almost identical PCs one a Surface Pro 7 and the other a Surface Pro 8. I have had a *lot* of issues trying to sync between these two. I keep getting spurious old data (bookmarks etc), regardless of what I do. I have tried this: Both computers logged out from Sync. On the computer I want to keep the current settings on and send to other computer - set all bookmarks, logins etc as wanted - log in to Sync and sync - log out of sync. On second computer which I want to be identical to first one, log in to sync - wait a while - log out of sync. This sort of works, but there are always extra items and/or some items that didn't seem to sync correctly. There are always extra bookmarks that neither computer started with, and, duplicated entries in passwords and login data. Question 1: how do I 'clear out' all data currently held by Sync so I can start fresh? Question 2: if the answer to question 1 is to delete firefox account and recreate, then, would the above procedure work correctly without extra's and duplicates? I feel the term 'Sync' is misused in firefox when spurious old data not on either machine is introduced to both when syncing. In my opinion, a better way to achieve everything would be to have an option to 'clear and copy' from this computer so that on any other computer, you can be sure of identical data after sync.