Style.posTop In Firefox

I cannot get Firefox 2.0.0.4 to reposition an object by changing the top of posTop attribute of the objects style. This workins in IE and Safari, but not Firefox.

function findPos(obj) {
var curleft = curtop = 0;
if (obj.offsetParent) {
curleft = obj.offsetLeft
curtop = obj.offsetTop
while (obj = obj.offsetParent) {
curleft += obj.offsetLeft
curtop += obj.offsetTop
}
}
return [curleft,curtop];
}

function ProposalInfoRollOver(id, obj) {
position = findPos(obj);

floater = document.getElementById('floater_'+id);
floater.style.display = 'block'
floater.style.posTop = (position[1]+8);
floater.style.posLeft = (position[0]-floater.offsetWidth+1);
}