I cloned my 2017 intel iMac onto an M2 Macbook Air. Since one week I use them independently and keep Firefox synchronized. I changed their names in Firefox sync. But under "connected devices" at first there was only one of them, depending on which one I refreshed the open window first. I tried to separate them by logging out and in again, but now both are gone in the list. Nevertheless, syncing works. I hope my Mozilla account won't get garbled up.