Submitting form fails on Mozilla

When trying to submit a form with taht contains a FCKEditor, Mozilla throws the following error:

sXHTML has no properties
File: /fckeditor/editor/js/fckeditorcode_gecko_1.js

The error occurs here:

return sXHTML.substr(7, sXHTML.length - 15);

I tracked it down to :

var sXHTML=this.MainNode.xml;

this.MainNode doesn't have an attribute called 'xml',
that's why sXHTML is undefined.

Hope that helps....