Firefox hides the ?xml processing instruction

When I was testing the DOM handling of the XML processing instructions in various browsers, I've found an interesting inconsistency: Internet Explorer includes the <?xml ?> processing instruction in the DOM tree, while Firefox hides it.

For example, when the following XML document ...

<?xml version="1.0" encoding="windows-1250"?>

<?xml-stylesheet href="countryPage.xsl" type="text/xsl"?>

<Test />

... is transformed into a DOM tree and processed with this JavaScript function:

function testPI(dom) {

  var topNodes = dom.childNodes;

  for (var i = 0; i < topNodes.length; i++) {

    var node = topNodes[i];

    wr("nodeType="+node.nodeType);

    if (node.nodeType == 7) {

      wr("PI="+node.target+" ... "+node.data);

    }

  }

... Internet Explorer generates the following text:

nodeType=7
PI=xml ... version="1.0" encoding="windows-1250"
nodeType=7
PI=xml-stylesheet ... href="countryPage.xsl" type="text/xsl"
nodeType=1

... while Firefox skips the <?xml ?> processing instruction:

nodeType=7
PI=xml-stylesheet ... href="countryPage.xsl" type="text/xsl"
nodeType=1