problem when using firefox browser need help

I've just finished searching on how to put at least 2 row of menus in my page but when I use Firefox browser I found out that it has a problem and returns a random result each time I reload it. This does not happen in the windows internet explorer.



I used these codes to make the rows.

<table>
<tr>
<td>100</td>
</tr>
<tr>
<td>400</td>
</tr>
</table>