title: ThunderBird Event for Viewing a Message
body: <p>I'm trying to modify a message before it is displayed in the main window in Thunderbird.  I can't seem to find 1) An event that will be triggered when a new message is opened/viewed 2) A way to modify the displayed contents of a message.</p>
  
  <p>I believe I need the <code>chrome://messenger/content/messenger.xul</code> overlay, and can use a listener such as:</p>
  
  <pre><code>window.addEventListener( "SOME MAGIC HERE", modify_message_handler, true );
  </code></pre>
  
  <p>But what that event is, I am unsure, along with what object I will get (a message header?) and how easily I can modify what is displayed.</p>
  
  <p>So the questions are:</p>
  
  <ul>
  <li>Do I have the correct overlay?</li>
  <li>Can this be done with events?  If not, how?</li>
  <li>If so, what event is needed and what object does it pass?</li>
  </ul>