code: function getPrefs(app) {
    // Default and only Firefox supported for the moment
    if (!app) {
      app = "firefox";
    }
  
    var appPrefs = prefs["DEFAULT_" + app.toUpperCase() + "_PREFS"];
    var commonPrefs = prefs.DEFAULT_COMMON_PREFS;
  
    return extend({}, commonPrefs, appPrefs);
  }
docs: Takes an app string ("firefox") and returns the merged preferences
  of common prefs with app-specific prefs as an object
  
  @param {String} app
  @return {Object}