I don't think that's how prototypes work in JavaScript though. The newly created objects refer to a chain of prototype references, and changes to the underlying prototypes will affect already existing objects.
My example was a simple one, and you are right, Javascript objects contain a reference to their prototype object from which they are cloned and via which they can inherit behavior. However, this is handled a bit differently in Self and in the original Tivoli Systems actors. The details between these systems are different so my example left out many interesting details.