Java Script a -moz-opacity

Chtěl jsem se zeptat jetli nejde pomocí js změnit vlastons nějakéko elementu -moz-opacity nebo taky jine vlastnosti -moz páč mě to nejde diky moc.

tady je script

var id, op = 100, step = -1;
id = window.setTimeout("Move()", 500);

function Move()
{
op += step;

if (op < 0) {
op = 0;
step = -step;
}

if (op > 100) {
op = 100;
step = -step;
}
document.getElementById("pres").filters.Alpha.opacity = op;
document.getElementById("ban").filters.Alpha.opacity = 100-op;

document.getElementById("pres").style.MozOpacity = op/100;
document.getElementById("pres").style.MozOpacity = 1-(op/100);

if(document.getElementById("ban").filters.Alpha.opacity ==100){
}
else{
id = window.setTimeout("Move()", 20);
}
}

var id, op = 100, step = -1;
id = window.setTimeout("Move()", 500);

function Move()
{
op += step;

if (op < 0) {
op = 0;
step = -step;
}

if (op > 100) {
op = 100;
step = -step;
}
document.getElementById("pres").filters.Alpha.opacity = op;
document.getElementById("ban").filters.Alpha.opacity = 100-op;

document.getElementById("pres").style.MozOpacity = op/100;
document.getElementById("ban").style.MozOpacity = 1-(op/100);

if(op==0){
}
else{
id = window.setTimeout("Move()", 20);
}
}

uz to mam

var id, op = 100, step = -1;
id = window.setTimeout("Move()", 500);

function Move()
{
op += step;

if (op < 0) {
op = 0;
step = -step;
}

if (op > 100) {
op = 100;
step = -step;
}
if(document.all){
document.getElementById("pres").filters.Alpha.opacity = op;
document.getElementById("ban").filters.Alpha.opacity = 100-op;
}
else{
document.getElementById("pres").style.opacity = op/100;
document.getElementById("ban").style.opacity = 100-(op/100);
}

if(op==0){
}
else{
id = window.setTimeout("Move()", 20);
}
}