JavaScript Constructor.prototype.method saves memory

gistfile1.js

'use strict';

// 56 MB in Chrome using JavaScript Console > Profiles > Take Heap Snapshot.
// 117 MB in Firefox viewing the URL about:memory.
function A() {
  this.b = function() {
    alert('yo');
  };
}
var a = [];
for (var i = 0; i < 1000000; i++) {
  a.push(new A());
}

// 18 MB in Chrome.
// 71 MB in Firefox.
function A() {}
A.prototype.b = function() {
  alert('yo');
};
var a = [];
for (var i = 0; i < 1000000; i++) {
  a.push(new A());
}

// 6 MB in Chrome.
// 26 MB in Firefox.
var a = [];
for (var i = 0; i < 1000000; i++) {
  a.push(i);
}

// 1 MB in Chrome.
// Not listed in Firefox. Zero?
// Nothing.