ZammadChat.prototype.isRetina = function() {
      var mq;
      if (window.matchMedia) {
        mq = window.matchMedia('only screen and (min--moz-device-pixel-ratio: 1.3), only screen and (-o-min-device-pixel-ratio: 2.6/2), only screen and (-webkit-min-device-pixel-ratio: 1.3), only screen  and (min-device-pixel-ratio: 1.3), only screen and (min-resolution: 1.3dppx)');
        return mq && mq.matches || (window.devicePixelRatio > 1);