title: What can cause a window.open to return "undefined"?
body: <p>I have the following script in my Xul app:</p>
  
  <pre><code>MyClass = function() {
   this.go = function() {
    try {
     var scanWindow = window.open('chrome://test/content/scanWindow.xul','Scan','chrome, width=850, height=150, centerscreen');
     dump("scanWindow = " + scanWindow); // console output in Xul
    } catch(err) {
     dump("ERROR: " + err); // console output in Xul
    }
      }
  }
  </code></pre>
  
  <p>when I call this method it prints</p>
  
  <blockquote>
    <p>scanWindow = undefined</p>
  </blockquote>
  
  <p>Any hint on what can be causing that?</p>