Incompatibilità browser

<script Language="Javascript">
   /* gestione del menu */
   function mmenu(ID) {
      var menu = document.getElementById(ID);
      var display = menu.style.display;
      menu.style.display = (display == "block") ? "none" : "block";
   menu.parentNode.style.listStyleImage = (display == "block") ? "url(cartellachiusa.gif)" : "url(cartellaaperta.gif)";         
   }
   
   /* inizializzazione del menu */
   window.onload = function() {
      var uls = document.getElementsByTagName("ul");
      for (i=0;i<uls.length;i++) {
         if(uls[i].getAttribute("class")=="submenu")uls[i].style.display = "none";
         if(uls[i].getAttribute("id") && uls[i].getAttribute("id").search("submenu-")!= -1) uls[i].style.display = "none";
      }
   }
</script>

<ul>
<?
$giustoex = explode(",", $giusto);
for($i = 0; $i < count($giustoex)-1; $i++){
   echo "<tr><td width=\"50%\" align=\"left\" valign=\"middle\">";
   echo "<li class=\"menu\"<a href=\"javascript:mmenu('submenu-$i')\">+</a>";
   echo "$giustoex[$i]";
   echo "<ul class=\"submenu\" id=\"submenu-$i\">";
   }
$sqlabb = "SELECT titolo, modered, modegreen FROM temp_abb WHERE id_utenti_online = \"$row[1]\" AND editore = \"$giustoex[$i]\" ORDER BY titolo, modered, modegreen";
$resultabb = mysql_query( $sqlabb ) or die (mysql_error());
while($rowabb = mysql_fetch_row($resultabb)){
   if($rowabb[1] == 1 || $rowabb[2] == 1){
      if($rowabb[1] == 1 && $rowabb[2] == 0)
         echo "<li><span style=background-color:red>$rowabb[0]</span></li>";         
      if($rowabb[1] == 0 && $rowabb[2] == 1)
         echo "<li><span style=text-decoration:underline>$rowabb[0]</span></li>";
      if($rowabb[1] == 1 && $rowabb[2] == 1)
         echo "<li><span style=text-decoration:underline><span style=background-color:red>$rowabb[0]</span></span></li>";
   }else echo "<li>$rowabb[0]</li>";   
}
echo "</ul></li></td></tr>";
?>
</ul>