import Firebase
import FirebaseInstanceID
import FirebaseMessaging
func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {

    registerForPushNotifications(application)
    FIRApp.configure()

    // Add observer for InstanceID token refresh callback.
    NSNotificationCenter
     .defaultCenter()
     .addObserver(self, selector: #selector(AppDelegate.tokenRefreshNotificaiton),
                                                     name: kFIRInstanceIDTokenRefreshNotification, object: nil)

    // Override point for customization after application launch.
    return true
  }

func registerForPushNotifications(application: UIApplication) {
      let settings: UIUserNotificationSettings =
        UIUserNotificationSettings(forTypes: [.Alert, .Badge, .Sound], categories: nil)
      application.registerUserNotificationSettings(settings)
      application.registerForRemoteNotifications()
  }


  func application(application: UIApplication, didReceiveRemoteNotification userInfo: [NSObject : AnyObject],
                   fetchCompletionHandler completionHandler: (UIBackgroundFetchResult) -> Void) {
    print("===== didReceiveRemoteNotification ===== %@", userInfo)
  }


 func tokenRefreshNotificaiton(notification: NSNotification) {
    let refreshedToken = FIRInstanceID.instanceID().token()!
    print("InstanceID token: \(refreshedToken)")

    // Connect to FCM since connection may have failed when attempted before having a token.
     connectToFcm()
  }

  func connectToFcm() {
    FIRMessaging.messaging().connectWithCompletion { (error) in
      if (error != nil) {
        print("Unable to connect with FCM. \(error)")
      } else {
        print("Connected to FCM.")
      }
    }
  }

Também a ser feito em Info.plist FirebaseAppDelegateProxyEnabled = NO

Não sei por enquanto, mas obtive a impressão (...) em didReceiveRemoteNotification, mas não recebi o pop-up. Envio a mensagem do Firebase -> Console -> Notificação -> Único dispositivo e copio aqui o token que recebi do xCode Console -> func tokenRefreshNotificaiton

Obtenha o próximo no console, mas não seja pop-up

<FIRAnalytics/INFO> Firebase Analytics enabled
InstanceID token: TOKEN_ID
Connected to FCM.
===== didReceiveRemoteNotification ===== %@ [notification: {
    body = test;
    e = 1;
}, collapse_key: com.pf.app, from: 178653764278]

Também configurações de aplicativos