What is the 'Firefox Account' the new sync system uses and how does it differ from Persona? Will I need a 'Firefox Account' for other Mozilla services? What about Firefox OS? It seems bizarre to me to have this additional account system while promoting Persona as the system for other people to use. Is Persona abandoned?

Edit: the article mentions a Firefox Account is needed to use the Firefox Marketplace too. That's a webapp which I thought would have suited Persona.