Most web developers use the navigator.userAgent to determine which browser is currently running your script. I've also seen this var IE = document.all ? true : false; But there is an undocumented library in the MS Ajax libraries for this... HEY PRESTO ----> Sys.Browser An example of this... if (Sys.Browser.agent != Sys.Browser.InternetExplorer) { //let's do something because we're not IE } Hope   read more »