An explanation of `__proto__` using an example and a `__proto__` "polyfill" for MSIE 9 & 10.

__proto__.js

  function Collection() {
		this.push.apply( this, arguments );
	}
	
	Collection.prototype = [];
	
	Collection.prototype.push = function( item ) { // we need to wrap this.push in a function or we'll get a recursion error from 
		if ( arguments.length > 1 ) {          // the arguments.length always being > 1 since the Array index is passed to the iterator
			this.slice.call( arguments ).map( function( val ) { this.push( val ); }, this );
			return this.length;
		}
		
		console.log( 'pushing: ', item );
		
		var proto_collection = this.__proto__,             // this is the prototype of the class we're in, i.e. Collection.prototype
			proto_array  = proto_collection.__proto__; // this is the super class, i.e. the new Array we assigned to Collection.prototype on line 5.
			
		return proto_array.call( this, item );
	}
	
	// this will make __proto__ available in MSIE 9 & 10
	;!function( item ) {
		if ( ( !( '__proto__' in item ) ) {                             // NOTE: Never put the `writable` property in an accessor descriptor
			Object.defineProperty( Object.prototype, '__proto__', { // not even as `false` as it b0rks the goddamn definition
				configurable : true,                            // see: https://plus.google.com/117400647045355298632/posts/YTX1wMry8M2
				enumerable   : false,
				get          : function() {
					return Object.getPrototypeOf( this );
				}
			} );
		}
	}( {} );