title: d3.event.path undefined in firefox
body: <p>I used d3.js to bind a click event to some svg-elements. I am trying to use d3.event.path to see the propagation path (elements below the clicked position) when an element is clicked. </p>
  
  <p>This works in chrome, but not in firefox (latest version, tried both windows 10, ubuntu 14.04).  Firefox returns undefined. </p>
  
  <p>Any idea how to get the propagation path of a d3 event and firefox ?</p>
  
  <pre><code>&lt;div id="test" style='width:200px;height:200px;border:2px solid black'&gt;
  &lt;/div&gt;
  
  var svg = d3.select('#test')
      .append('svg')
      .attr('width', 200).attr('height', 200);
  
  var r = svg.append('rect')
      .attr('transform', 'translate(50,50)')
      .attr('width', 100).attr('height', 100)
      .style('fill', 'purple');
  
  svg.on('click', function(){
      console.log(d3.event.path);
  });
  </code></pre>
  
  <p>see <a href="https://jsfiddle.net/a9L9j9j1/" rel="nofollow">https://jsfiddle.net/a9L9j9j1/</a>  for an example. When clicking the purple rectangle chrome correctly returns an array [rect, svg, div ...  window], but firefox returns undefined.</p>
  
  <p>Thanks!</p>