When a supersite is scaled down in height so that borders are shown on left and right side ( current width has to be smaller than the page width of the design ) then the mouse over effects do not work in Firefox and Internet Explorer. They do work in Chrome and Opera.
It works when the following code is changed in function xr_mm:
...
if (xr_ms > 0) {
...
if (xr_scale && !xr_spaold) {
if (!xr_chrome) {
if (xr_scof) {
...
} else {
x = (x-((xr_xr.parentNode.offsetWidth-(xr_xr.offsetWidth*xr_scale))/2)+xr_dx)/xr_scale;//** error correction, before: xr_ox + ((x - xr_ox) / xr_scale);

The error correction might be simpler but I wanted to limit the change to one single line.