Add loadXML, selectNodes and selectSingleNode functions for Firefox

var infoNodes;
if(document.all)
infoNodes = document.getElementById("xmlInfo").XMLDocument.documentElement.selectNodes("Product");
else{
XMLDocument.prototype.loadXML = function(xmlString)
{
var childNodes = this.childNodes;
for (var i = childNodes.length - 1; i >= 0; i--)
this.removeChild(childNodes[i]);

var dp = new DOMParser();
var newDOM = dp.parseFromString(xmlString, "text/xml");
var newElt = this.importNode(newDOM.documentElement, true);
this.appendChild(newElt);
};

// check for XPath implementation
if( document.implementation.hasFeature("XPath", "3.0") )
{
// prototying the XMLDocument
XMLDocument.prototype.selectNodes = function(cXPathString, xNode)
{
if( !xNode ) { xNode = this; }
var oNSResolver = this.createNSResolver(this.documentElement)
var aItems = this.evaluate(cXPathString, xNode, oNSResolver,
XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null)
var aResult = [];
for( var i = 0; i < aItems.snapshotLength; i++)
{
aResult[i] =  aItems.snapshotItem(i);
}
return aResult;
}

// prototying the Element
Element.prototype.selectNodes = function(cXPathString)
{
if(this.ownerDocument.selectNodes)
{
return this.ownerDocument.selectNodes(cXPathString, this);
}
else{throw "For XML Elements Only";}
}
}

// check for XPath implementation
if( document.implementation.hasFeature("XPath", "3.0") )
{
// prototying the XMLDocument
XMLDocument.prototype.selectSingleNode = function(cXPathString, xNode)
{
if( !xNode ) { xNode = this; }
var xItems = this.selectNodes(cXPathString, xNode);
if( xItems.length > 0 )
{
return xItems[0];
}
else
{
return null;
}
}

// prototying the Element
Element.prototype.selectSingleNode = function(cXPathString)
{   
if(this.ownerDocument.selectSingleNode)
{
return this.ownerDocument.selectSingleNode(cXPathString, this);
}
else{throw "For XML Elements Only";}
}
}

// 创建 XML 文档对象
var xmlRef = document.implementation.createDocument("text/xml", "", null);
// 使用 importNode 将HTML DOM 的一部分转换为XML 文档。
// 参数 true 表示克隆全部子元素。
var myNode = document.getElementById("xmlInfo");
xmlRef.loadXML(myNode.innerHTML);
infoNodes = xmlRef.documentElement.childNodes;
}

Source: http://www.cnblogs.com/skyover/archive/2005/12/03/290055.html

See Also: Firefox compatible xPath functions in JavaScript