code: function encode(fp) {
    return new Promise((resolve, reject) => {
      fp.encode((err, encoded) => {
        if (err) {
          reject(err);
  
          return;
        }
        resolve(encoded);
      });
    });
  }
docs: denodeifies FirefoxProfile.encode
  @param {FirefoxProfile} fp
  @returns {Promise<string>}