XSL/XML Transform Object In Firefox

I'm having problems with a custom JS object (XMLLoadObject) I designed
to load XML and XSL files, perform an XSL transform with them and embed
the resultant HTML fragment into the host HTML document. I designed this
object so that I could generate and embed HTML fragments from more than
one XML/XSL source into a single HTML document. This is done by
instantiating an XMLLoadObject with an XML filename, an XSL filename,
and the ID of the HTML element as arguments. Once the object is created,
XSL Parameters can be assigned to the transformation with a member
function. Finally the documents are loaded and transformed with call to
the member function xmlLoad(). A distinct object must be instantiated
for each transform. The object assigns closured member functions as
event handlers to give access to the object's XML Document and XSL
Document objects (member data). Code: