layers i netscape

Hvorfor virker denne funktion ikke i netscape!!?

<script language="javascript">
<!-- 

function vis_lag(lag_id) {
if(document.layers) {
document.lag_id.visibility="show";
document.lag_txt_0.visibility="hide"}
else {if (document.all)lag_id.style.visibility="visible";
lag_txt_0.style.visibility="hidden"}
}


function skjul_lag(lag_id) {
if(document.layers) document.lag_id.visibility="hide";
if(document.layers) document.lag_txt_0.visibility="show";
else {if (document.all)lag_id.style.visibility="hidden";
lag_txt_0.style.visibility="visible"}
}

//-->
</script>

<a href="#" target="_top" onMouseOver="vis_lag(lag_txt_1)"; onMouseOut="skjul_lag(lag_txt_1);"><img src=""></a>

<div id="lag_txt_0" style="position:absolute; left:91; top:22; width:180px; height:80; z-index:0; visibility: visible"><font face="arial" size="4">text</font></div>

<div id="lag_txt_1" style="position:absolute; left:91; top:22; width:180px; height:80; z-index:1; visibility: hidden;">bla</div>