Sapete spiegarmi xkè il codice sotto in IE funziona e in Firefox no??? O almeno non funzia correttamente.

Ho privato anche con visibility:hidden/visible oltre a display:block(inline)/none

ciao e grazie


<script> function al(){
alert(document.getElementById('a').style.display);
if (document.getElementById('a').style.display=='none '){document.getElementById('a').style.display='blo ck'}
else
{document.getElementById('a').style.display='none' }
}
</script>
<body>
<table >
<tr>
<td style="border-style: solid; border-width: 1px"></td>
<td style="border-style: solid; border-width: 1px"></td>
<td style="border-style: solid; border-width: 1px"></td>
<td style="border-style: solid; border-width: 1px"></td>
</tr>
<tr id="a" style="display:none">
<td style="border-style: solid; border-width: 1px">gggggggggggggggggggg</td>
<td style="border-style: solid; border-width: 1px"></td>
<td style="border-style: solid; border-width: 1px"></td>
<td style="border-style: solid; border-width: 1px"></td>
</tr>
<tr>
<td style="border-style: solid; border-width: 1px">
<input type="button" value="Pulsante" name="B3" onclick="al()">
</td>
<td style="border-style: solid; border-width: 1px"></td>
<td style="border-style: solid; border-width: 1px"></td>
<td style="border-style: solid; border-width: 1px"></td>
</tr>
</table>

</body>