I need to feed xml content to a function.

I did the following code,

// initialized xmlDoc by identifying browser
xmlDoc.load("xmlFile.xml");
alert(xmlDoc.documentElement.xml);

It works fine in IE but not in mozilla.
alert(xmlDoc.documentElement) returns an Object Element
but alert(xmlDoc.documentElement.xml) returns null

Is there any similar functionalities that work in mozilla.

Please Help.