Sync doesn't work for passwords
I remove login/password, press "sync" button a million times and every possible device, but other devices still show the login I removed...
AFAIK all devices must be one and connected to the Firefox account and left running so sync has time to reconnect and update the data. Sync isn't a backup system only sync data between devices so if one delete data in another it removes the data in the sync. So if devices are off not logged into Firefox account sync doesn't work.