var agt = navigator.userAgent.toLowerCase();
var appVer = navigator.appVersion.toLowerCase();
var iePos = appVer.indexOf("msie");

var isMinor  = parseFloat(appVer);
var isMajor  = parseInt(isMinor);

var isOpera  = (agt.indexOf("opera") != -1);
var isOpera7 = (agt.indexOf("opera 7") != -1 || agt.indexOf("opera/7") != -1);
var isSafari = (agt.indexOf("safari") != -1);
var isGecko  = (agt.indexOf("gecko") != -1 && !isSafari);
var isAOL    = (agt.indexOf("aol") != -1);
var isAOL8   = (agt.indexOf("aol 8") != -1);
var isIE     = (iePos != -1 && !isOpera);
if (iePos != -1) {
  isMinor = parseFloat(appVer.substring(iePos + 5, appVer.indexOf(";",iePos)));
  isMajor = parseInt(isMinor);
}
isIE4 = (isIE && isMajor == 4);
isIE5 = (isIE && isMajor == 5);
isIE6 = (isIE && isMajor == 6);
isIE7 = (isIE && isMajor == 7);

var supported = isIE5 || isIE6 || isIE7 || isGecko || isAOL8 || isOpera7 || isSafari;