Javascript cross-domain web request fails with Status=0?

EDIT: It's been pointed out below that this doesn't work because craigslist doesn't set an Allow-Cross-Domain header. OK, I'll buy that. Is there any other way to use javascript in firefox to download a page cross-domain then?

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Yes, I know the following code does not work in IE. I know IE expects me to use XDomainRequest() instead. I don't care about that. This is firefox only.

I'm trying to do a cross-domain web request in firefox javascript. I keep getting a status of 0. Does anyone know why?

var url = "http://newyork.craigslist.org";
var xdr = new XMLHttpRequest(); //Yes, I know IE expects开发者_运维百科 XDomainRequest. Don't care
xdr.onreadystatechange = function() { 
  if (xdr.readyState == 4) {
      alert(xdr.status); //Always returns 0! And xdr.responseText is blank too
  }
}
xdr.open("get", url, true);
xdr.send(null);

Shouldn't that work?

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Craigslist doesn't allow cross-domain requests to it. It needs to send a proper Access-Control-Allow-Origin header.