ok risolto con
codice:
// tutti i browser
if (typeof window.innerWidth != 'undefined')
{
lar_finestra = window.innerWidth;
alt_finestra = window.innerHeight;
}
// IE6 in standards compliant mode (i.e. with a valid doctype as the first line in the document)
else if (typeof document.documentElement != 'undefined'
&& typeof document.documentElement.clientWidth !=
'undefined' && document.documentElement.clientWidth != 0)
{
lar_finestra = document.documentElement.clientWidth,
alt_finestra = document.documentElement.clientHeight
}
// older versions of IE
else
{
lar_finestra = document.getElementsByTagName('body')[0].clientWidth,
alt_finestra = document.getElementsByTagName('body')[0].clientHeight
}