You will need to post the JS code...noting that this is not a JS forum
But its likely in the way that you are defining the form
by detecting the browser with this:
// uses object detection technique to determine client browser
var isNav4 = document.layers; // checks for Netscape Navigator 4
var isNS6 = (document.getElementById && !document.all); // checks for Netscape 6 or higher
var isIE4 = (document.all && !document.getElementById); // checks for Internet Explorer 4
var isIE5 = (document.all && document.getElementById); // checks for Internet Explorer 5 or higher
then changing the code to match the browser, you should be able to get it fixed