title: Verifying sent messages Firefox addon SDK
body: <p>I have a question. I have a panel in Firefox add-on and I would like to modify things on the page when it is closed. I created a listener on the panel and a content script <code>close.js</code> that will modify the the page.</p>
  
  <pre><code>panel.port.on("close", function() {
      panel.port.emit("close");
  });
  </code></pre>
  
  <p>What I would like to know is how can I debug and verify that the message "close" has effectively been sent  ? Because now it is not working but I have no possibility of checking what messages has been sent ?</p>
  
  <p>Do I have to load <code>close.js</code> as a contentScript when I create the panel ? Knowing that there are other scripts that modify the page that are not loaded when creating the panel...</p>