title: Empty "for" loop in Facebook ajax
body: <p>While surfing facebook and using the Firebug network debugger I noticed that facebook's AJAX responses all start with an empty for loop.</p>
  
  <p>Example:</p>
  
  <pre><code>for(;;);{...}
  </code></pre>
  
  <p>Does anyone know why this is done?  I assume it's to prevent some sort of XSS attack but I don't totally understand. Thanks!</p>