title: evaluate().singleNodeValue return null in Firefox
body: <p>I'm using <code>Range</code> and <code>XPATH</code> to retreive, save and rebuild position in html files. to rebuild range, i'm using <code>document.evaluate().singleNodeValue</code>, the problem is that singleNodeValue is returning null on firefox, it work well on chrome. Any idea why ? here my code:</p>
  
  <pre><code>fonction rebuildRange(xpath){
  
      var selectionDetails = xpathh;
      selectionDetails = selectionDetails.split(/\|/g);
      var range = oDoc.createRange();
      var selectionDetails0 = selectionDetails[0];
      selectionDetails0 = selectionDetails0.replace(/\//g, "/h:");
      selectionDetails0 = selectionDetails0.replace("h:t", "t");
      var selectionDetails2 = selectionDetails[2];
      selectionDetails2 = selectionDetails2.replace(/\//g, "/h:");
      selectionDetails2 = selectionDetails2.replace("h:t", "t");
  
      range.setStart(oDoc.evaluate(selectionDetails0, oDoc, nsResolver, 9, null).singleNodeValue, Number(selectionDetails[1]));
      range.setEnd(oDoc.evaluate(selectionDetails2, oDoc, nsResolver, 9, null).singleNodeValue, Number(selectionDetails[3]));
  }
  </code></pre>