this is one of most mystery feature in JavaScript, after assigning the object method to other variable, the binding (this keyword) is lost

var john = {
  name: 'John',
  greet: function(person) {
    alert("Hi " + person + ", my name is " + this.name);
  }
};

john.greet("Mark"); // Hi Mark, my name is John

var fx = john.greet;  
fx("Mark"); // Hi Mark, my name is 

my question is:

1) what is happening behind the assignment? var fx = john.greet; is this copy by value or copy by reference? fx and john.greet point to two diferent function, right?

2) since fx is a global method, the scope chain contains only global object. what is the value of this property in Variable object?