title: Why does canvas.toDataURL() throw a security exception?
body: <p>Did I not get enough sleep or what? This following code</p>
  
  <pre><code>var frame=document.getElementById("viewer");
  frame.width=100;
  frame.height=100;
  
  var ctx=frame.getContext("2d");
  var img=new Image();
  img.src="http://www.ansearch.com/images/interface/item/small/image.png"
  
  img.onload=function() {
      // draw image
      ctx.drawImage(img, 0, 0)
  
      // Here's where the error happens:
      window.open(frame.toDataURL("image/png"));
  }
  </code></pre>
  
  <p>is throwing this error: </p>
  
  <pre><code>SECURITY_ERR: DOM Exception 18
  </code></pre>
  
  <p>There's no way this shouldn't work! Can anyone explain this, please?</p>