docs: function installProfile(firefox, env) {
    var installed = promise.defer();
    child.exec(firefox + ' -silent', {env: env, timeout: 180 * 1000},
        function(err) {
          if (err) {
            installed.reject(new Error(
                'Failed to install Firefox profile: ' + err));
            return;
          }
          installed.fulfill();
        });
    return installed.promise;
  }