title: document.createEvent fails
body: <p>The following code fails (in javascript console, and also when injecting a script via browser extension)</p>
  
  <pre><code>document.createEvent('TestEvent')
  </code></pre>
  
  <p>Firebug spits out:</p>
  
  <pre><code>[Exception... "Operation is not supported" 
   code: "9" 
   nsresult: "0x80530009 (NS_ERROR_DOM_NOT_SUPPORTED_ERR)" 
   location: "http://www.google.com 
   Line: 71"] 
  </code></pre>
  
  <p>Chrome gives a similar error message. What am I doing wrong?</p>