code: function(opt_dir) {
    /** @private {!Object} */
    this.preferences_ = {};
  
    mixin(this.preferences_, getDefaultPreferences()['mutable']);
    mixin(this.preferences_, getDefaultPreferences()['frozen']);
  
    /** @private {boolean} */
    this.nativeEventsEnabled_ = true;
  
    /** @private {(string|undefined)} */
    this.template_ = opt_dir;
  
    /** @private {number} */
    this.port_ = 0;
  
    /** @private {!Array.<string>} */
    this.extensions_ = [];
  }
docs: Models a Firefox proifle directory for use with the FirefoxDriver. The
  {@code Proifle} directory uses an in-memory model until {@link #writeToDisk}
  is called.
  @param {string=} opt_dir Path to an existing Firefox profile directory to
  use a template for this profile. If not specified, a blank profile will
  be used.
  @constructor