Non avevo pensato che il problema potesse essere altrove. Aggiungo la pagina HTML che comprende anche la funzione javascript usata per richiamare i <div>
codice:
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
<title>Documento senza titolo</title>
<link rel="stylesheet" href="foglio5.css" type="text/css" />
<!--[if IE]>
<link rel="stylesheet" href="foglioIE.css" type="text/css" />
<![endif]-->
<script type="text/Javascript">
<!--
function MM_findObj(n, d) { //v4.01
var p,i,x; if(!d) d=document; if((p=n.indexOf("?"))>0&&parent.frames.length) {
d=parent.frames[n.substring(p+1)].document; n=n.substring(0,p);}
if(!(x=d[n])&&d.all) x=d.all[n]; for (i=0;!x&&i<d.forms.length;i++) x=d.forms[i][n];
for(i=0;!x&&d.layers&&i<d.layers.length;i++) x=MM_findObj(n,d.layers[i].document);
if(!x && d.getElementById) x=d.getElementById(n); return x;
}
function MM_showHideLayers() { //v6.0
var i,p,v,obj,args=MM_showHideLayers.arguments;
for (i=0; i<(args.length-2); i+=3) if ((obj=MM_findObj(args[i]))!=null) { v=args[i+2];
if (obj.style) { obj=obj.style; v=(v=='show')?'visible': (v=='hide')?'hidden':v; }
obj.visibility=v; }
}
//-->
</script>
<link rel="shortcut icon" href="pag1on.ico" />
</head>
<body marginwidth="0" marginheight="0" onload="MM_showHideLayers('fermeture','','hide','text','','hide','text2','','hide','bas','','hide')">
<div id="box">
<div id="fermeture">[img]fermeture.jpg[/img]
<map name="Map" id="Map"><area shape="rect" coords="745,4,801,14" href="#" onclick="MM_showHideLayers('fermeture','','hide','text','','hide','text2','','hide','bas','','hide')" /></map></div>
<div id="text">
</div>
<div id="text2"><!--il problema riguarda questi due div, (ce ne sono anche altri due ma qui
non sono scritti); la barra appare in firefox per mac anche quando sono in posizione 'hidden'-->
</div>
<div id="bas">
</div>
</div>
<table class="menu" cellpadding="0" cellspacing="0">
<tr>
<td class="logo">[img]onverra.jpg[/img]</td>
<td class="cella">
<div class="link">[img]pag1off.jpg[/img]<span style="background-color:#FF0000">[img]pag1on.jpg[/img]</span></div> </td>
<td class="cella">
<div class="link">[img]pag2off.jpg[/img]<span style="background-color:#FFFF00">[img]pag2on.jpg[/img]</span></div> </td>
<td class="cella">
<div class="link">[img]pag3off.jpg[/img]<span style="background-color:#00CC33">[img]pag3on.jpg[/img]</span></div> </td>
<td class="cella">
<div class="link">[img]pag4off.jpg[/img]<span style="background-color:#00CCFF">[img]pag4on.jpg[/img]</span></div> </td>
</tr>
</table>
</body>
</html>
Grazie