Try this

<HTML>

<HEAD>

<TITLE>Cross Browser alert</TITLE>

<script language='javascript'>

var M='false';

var N='false';

function go(M,N)

{

if(M!='')

{

alert("Internet Explorer");

}

if (N!='')

{

alert("Netscape");

}

}

</script>

</HEAD>

<BODY>

<script language='javascript'>

var app=navigator.appName.substring(0,1);

if (app=='N')

{

N='true';

M='';

//document.writeln(''+N);

go(M,N);

}

else

{

M='true';

N='';

go(M,N);

}

</script>

<br />

<span id="pred" style="color:red">This is Red</span>

<script language='javascript'>

</script>

</BODY>

</HTML>