title: TypeError: Property 'handleEvent' is not callable IN FIREFOX
body: <p>I did a Google search about this before coming here, it may be a bug, but I would like a second opinion first, maybe I'm just writing the code wrong.</p>
  
  <p>I'm creating an audio player with custom controls. When I click the PLAY/PAUSE Button, I get this error:</p>
  
  <p>TypeError: Property 'handleEvent' is not callable.</p>
  
  <p>This error does NOT occur on my Rewind 10 Seconds Button OR my Loop Button</p>
  
  <p>HTML:</p>
  
  <pre><code>&lt;audio id="audio" controls style="width:800px;"&gt;
      &lt;source src="myAudio.mp3" type="audio/mp3"&gt;
  &lt;/audio&gt;
  
  &lt;div id="media-controls"&gt;
      &lt;button type="button" id="play-pause" class="paused" &gt;PLAY/PAUSE&lt;/button&gt;
      &lt;button type="button" id="rewind10" &gt;REWIND 10 SECONDS&lt;/button&gt;
      &lt;button type="button" id="loop" &gt;LOOP&lt;/button&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>JS:</p>
  
  <pre><code>var track = document.getElementById('audio');
  createControls();
  
  function createControls(){
          playPause = document.getElementById("play-pause");
          rewindBTN = document.getElementById("rewind10");
          loopBTN = document.getElementById("loop");
  
          playPause.addEventListener("click",playPause);
  
          loopBTN.addEventListener("click",loopToggle);
  
          rewindBTN.addEventListener("click",rewindTenSeconds);
  
      }
  
      function playPause(){
          if(track.paused){
              track.play();
          } else {
              track.pause();
          }
      }
  
      function rewindTenSeconds(){
          track.currentTime = track.currentTime - 10;
      }
  
      function loopToggle(){
          if (track.loop ==  false){
              track.loop = true;
          } else{
              track.loop = false;
          }
      }
  </code></pre>