Javascript global objects stops working after prototype change!

I don't if I am missing something obvious, but when I do something like below:-

Object.prototype.inherit = function(fromClass) {
  fromClass.apply(this, Array.prototype.slice.call(arguments, 1));

  for(var key in fromClass.prototype){
    if(typeof fromClass.prototype[key] == 'function')
        this.prototype[key] = fromClass.prototype[key];
  }
};

The开发者_开发百科n I can no longer work with any objects. I always get undefined. Similary when I try to 'inject' some method into Array.prototype then arrays stop working! I am using Firefox 4.0.1.

Am I missing something?

---

PLEASE, PLEASE, PLEASE, PLEASE DO NOT EXTEND OBJECT.PROTOTYPE.

Thank you.

Now getting on to your question, what do you mean you can no longer work with objects? You're going to break for-in loops, but short of that everything should still work.