JS Error in FireFox

Been getting this error in FireFox:

Error: this.DOMDocument has no properties
Source File: http://domain.iqdevs.com/_iq_rte/admin/ ... gecko_2.js
Line: 21

it occurs here......on this line of javascript.....

var FCKXml;if (!(FCKXml=NS.FCKXml)){FCKXml=NS.FCKXml=function(){};FCKXml.prototype.LoadUrl=function(urlToCall){var oFCKXml=this;var oXmlHttp=FCKTools.CreateXmlObject('XmlHttp');oXmlHttp.open("GET",urlToCall,false);oXmlHttp.send(null);if (oXmlHttp.status==200) this.DOMDocument=oXmlHttp.responseXML;else if (oXmlHttp.status==0&&oXmlHttp.readyState==4) this.DOMDocument=oXmlHttp.responseXML;else alert('Error loading '+urlToCall+'');};FCKXml.prototype.SelectNodes=function(xpath,contextNode){var aNodeArray=new Array();var xPathResult=this.DOMDocument.evaluate(xpath,contextNode?contextNode:this.DOMDocument,this.DOMDocument.createNSResolver(this.DOMDocument.documentElement),XPathResult.ORDERED_NODE_ITERATOR_TYPE,null);if (xPathResult){var oNode=xPathResult.iterateNext();while(oNode){aNodeArray[aNodeArray.length]=oNode;oNode=xPathResult.iterateNext();};};return aNodeArray;};FCKXml.prototype.SelectSingleNode=function(xpath,contextNode){var xPathResult=this.DOMDocument.evaluate(xpath,contextNode?contextNode:this.DOMDocument,this.DOMDocument.createNSResolver(this.DOMDocument.documentElement),9,null);if (xPathResult&&xPathResult.singleNodeValue) return xPathResult.singleNodeValue;else return null;};}


any ideas?

thanks,
travis