Does anyone know how to make this code work in Mozilla?

function toggleT(_w,_h)
{
if (document.all)
{ // is IE

if (_h=='s') eval("document.all."+_w+".style.visibility='visibl e';");
if (_h=='h') eval("document.all."+_w+".style.visibility='hidden ';");
if (_h=='s') eval("document.all."+_w+".style.display='block';") ;
if (_h=='h') eval("document.all."+_w+".style.display='none';");