I've gone and tested this issue in IE, Chrome and Firefox.  Fails in all three.  In Firefox with Firebug, the javascript for 'onMouseOutParagraph' stopped to complain that reltg was 'undefined' in one case and was 'HTML' in another.  Also when the page first loads in Firefox, Firebug reports that $wnd.external.saxonErrorHandler is not a function.  Continuing on, the page loads and the onmouseout fails as described.  After modifying the javascript to check for null and 'HTML' instead of 'BODY', I now have a solution that works in all three browsers.  So with IE and Chrome, when the ixsl:call() invocation of my javascript throws an exception, is the saxonErrorHandler catching it and reporting that that the function doesn't exist?  

onMouseOutParagraph = function(e,p) {
    var reltg = (e.relatedTarget) ? e.relatedTarget : e.toElement;
while (reltg != null && reltg != p && reltg.nodeName != 'HTML')
reltg = reltg.parentNode;
if (reltg == p) return false;
   return true;
}