title: Find the source of an XMLHttpRequest using Chrome/Firefox dev tools
body: <p>I'm trying to debug a web application not written by me. There is a failing XMLHttpRequest being made:</p>
  
  <pre><code>XMLHttpRequest cannot load ... No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin '...' is therefore not allowed access. 
  </code></pre>
  
  <p>Is there a way, preferably using Chrome developer tools, to locate the source of this call?</p>