Function Works On IE But Not On Mozilla FF

Following function works for IE, but not for Mozilla FF. I am truncating the string to size =20. Also I am using custom attribute att as I have too many tags inside a <td>.

function trunc_dest()
{
var x = document.getElementById('chtbl');

var t = x.getElementsByTagName('tr');
for (var i = 0; i < t.length; i++)
{
var d = t[i].getElementsByTagName('td');
for (var j = 0; j < d.length; j++)
{
if (d[j].att == 'dest')
{
// var e = d[j].innerHTML;
var w_str = unescape(d[j].innerHTML).split('<');
// alert(w_str[0]);
if (parseInt(w_str[0].length) > 20)
{
d[j].innerHTML = w_str[0].substring(0,19)+"...*";
} } } }}