title: Way to debug CORS errors
body: <p>Every once in a while I have to debug cross-origin resource sharing related problems during web-development.</p>
  
  <p>To my testing, Chrome and Firefox give virtually no information when they cancel a request due to a CORS violation. Usually debugging involes checking the all the headers against specs, reading the CORS standard etc. It is a really cumbersome process.</p>
  
  <p>Isn't there a way to tell any Browser that it should be more verbose about <strong>why</strong> it canceled a specific request?</p>
  
  <p>For example, I rather have more verbose debug messages like <code>Request canceled due to missing X-Requested-With field in received Access-Control-Allow-Headers field</code> or <code>Request canceled because supplied Origin: and received Access-Control-Allow-Origin: fields mismatch</code>.</p>