probably simple! can't use string variable in window.location

x is a string variable that I can alert to myself and I know it's good. But for some reason window.location omits it. What am I not seeing?

function addProduct() {
var x = '?selection=<? echo $_GET['selection']; ?>&products=';
var frm = document.checkForm;
// Loop through all elements
for (i=1; i<frm.length; i++) {
if (frm.elements[i].checked == true) {
x += frm.elements[i].value + ',';
}
}
window.location='addItem.php'+x;
}

That technique worked fine for me.

x='?a=22222';
window.location='page.htm'+x; //took me page.htm?a=22222

Works in IE but not in FF?!?

I didn't try IE, worked in FF.

Not sure what changed, but as I was working on other things, it just started working. Maybe cache.