MyService extends FirebaseMessagingService

 public static final String EXTRA_NOTIFICATION_OBJECT = "com.xxx.yyy.EXTRA_NOTIFICATION_OBJECT";
 public static final String NOTIFICATION_PRIVATE = "com.xxx.yyy.permission.NOTIFICATION";

@Override
    public void onMessageReceived(RemoteMessage remoteMessage) {
      Intent i = new Intent(ACTION_SHOW_NOTIFICATION);
      i.putExtra(EXTRA_NOTIFICATION_OBJECT, "Hello World!");
      sendOrderedBroadcast(i, NOTIFICATION_PRIVATE, new BroadcastReceiver() {
      @Override
         public void onReceive(Context context, Intent intent) {
            if (getResultCode() == Activity.RESULT_OK) {
               buildNotification();
            }
         }
      }, null, Activity.RESULT_OK, null, null);
    }

MainActivity

    BroadcastReceiver mNotificationBroadcastReceiver;

     OnCreate
     mNotificationBroadcastReceiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                addCountToBell();
                setResultCode(Activity.RESULT_CANCELED);
                //tell the sender of the broadcast that it received the broadcast
            }
     };

    OnResume
    registerReceiver(mNotificationBroadcastReceiver, filter,
        MyService.NOTIFICATION_PRIVATE, null);

    onPause
    unregisterReceiver(mNotificationBroadcastReceiver);