kentbrew

// If we know the extension's ID and a path to one of its web-accessible resources, we can quietly check for presence.

(function (w, a) {
  var checkExt = function (callback) {
    var hazExt = false;
    var img = new Image();
    img.onload = function () {
      hazExt = true;
    };
    // need to know the right protocol for Firefox and Edge extensions