Found the problem...
Not all versions of IE support the scrolling position in the same way. Some use document.documentElement.scrollTop and some use document.body.scrollTop. So I've changed the A573X288.js file as follows (Col 1362):
if(cart_browser_ie)
{
if(document.documentElement.scrollTop)
{
qzp = event.clientX + document.documentElement.scrollLeft;
qzf = event.clientY + document.documentElement.scrollTop;
}
else
{
qzp = event.clientX + document.body.scrollLeft;
qzf = event.clientY + document.body.scrollTop;
}
}
else
{
qzp = qzim.pageX;
qzf = qzim.pageY;
}
Now works fine in IE and Firefox...
Thanks
Simon