Código HTML:
<html>
<head>
<title>Untitled</title>
<SCRIPT LANGUAGE="JavaScript">
function f()
{
var tabla = document.getElementById("tabla").getElementsByTagName('td');
for (el in tabla)
if (tabla[el].innerText=="xxx") alert(el);
}
</SCRIPT>
</head>
<body onload="f()">
<center>
<table id="tabla" border="1">
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>xxx</td></tr>
<tr><td>aaa</td></tr>
<tr><td>aaa</td></tr>
<tr><td>aaa</td></tr>
<tr><td>aaa</td></tr>
<tr><td>aaa</td></tr>
<tr><td>aaa</td></tr>
<tr><td>aaa</td></tr>
</table>
</center>
</body>
</html> Solo en FF no funciona
