Finding events on a page added using addEventListener

Hi,

I'm building a Javascript crawler using XULRunner as part of a
University project. Its easy to pull out all the element.on* events by
traversing the dom tree, however I'm having difficulties with the
addEventListener events. I can't find any interfaces that expose these
events, so I'm guessing the best way forward is to overwrite the
addEventListener function and redirect the arguments to an array
something like this:

Node.prototype.addEventListenerOld = Node.prototype.addEventListener;
Node.prototype.addEventListener = function(type, func, capture) {
  events.push({this, type, func, capture});
  return this.addEventListenerOld(type, func, capture);
}

This doesn't work however I can overide a single elements
eventlistener like so:

var z = browser.contentDocument.wrappedJSObject.getElementById("z");
z.addEventListenerOld = z.addEventListener;
z.addEventListener = function(type, func, capture) {
  events.push({this, type, func, capture});
  return z.addEventListenerOld(type, func, capture);
}

browser points to an <xul:browser>.

So my question is what would I need to overide to get this working for
all objects in my <xul:browser> element? Alternatively is there a
better method an interface I've missed. I'm open to any solutions this
is just a demo, so it doesn't matter if its insecure.

Sorry if this is the wrong group to post this, if it isn't it would be
great if you could point me in the right direction. ;)

Thanks,

Jon