isFirefox/isWebkit/isSafari

isFirefox

'use strict';

function isFirefox() {
  return /firefox/i.test(navigator.userAgent);
}

function isWebkit() {
  return 'WebkitAppearance' in document.documentElement.style;
}

function isSafari() {
  return !!window.safari;
}


if(navigator.appName.indexOf("Internet Explorer")!=-1){     //yeah, he's using IE
    var badBrowser=(
        navigator.appVersion.indexOf("MSIE 9")==-1 &&   //v9 is ok
        navigator.appVersion.indexOf("MSIE 1")==-1  //v10, 11, 12, etc. is fine too
    );

    if(badBrowser){
        // navigate to error page
    }
}