How to set Menu Size according to Browser in Java Script

// Some time programmer feels that menu width looks less or more as compare to looking in Mozilla and safari, for solving this problem 
// a programer can set the menu width according to the browser compatibility
function setMenuSize()
{
var mfund = document.getElementById("Mfund");
var brow=((navigator.appName) +
(parseInt(navigator.appVersion)));

//if(parseInt(navigator.appVersion >=4))
//{
if(brow == "Microsoft Internet Explorer4")
{
//alert('hi');
document.getElementById("a2").style.width = '150px';
}
}