__proto__ VS. prototype in JavaScript

This figure again shows that every object has a prototype. Constructor
function Foo also has its own __proto__ which is Function.prototype,
and which in turn also references via its __proto__ property again to
the Object.prototype. Thus, repeat, Foo.prototype is just an explicit
property of Foo which refers to the prototype of b and c objects.

var b = new Foo(20);
var c = new Foo(30);

What are the differences between __proto__ and prototype?

The figure was taken from dmitrysoshnikov.com.

Answer

__proto__ is the actual object that is used in the lookup chain to resolve methods, etc. prototype is the object that is used to build __proto__ when you create an object with new:

( new Foo ).__proto__ === Foo.prototype;
( new Foo ).prototype === undefined;