Different behavior of SW when sending using POSTMAN and via Notification composer. Steps to replicate:

1. Add firebase@9.0.2 to app


2. firebase-messaging-sw.js service-worker file in the public folder in our react app and add this code:

        // Scripts for firebase and firebase messaging
        importScripts('https://www.gstatic.com/firebasejs/9.0.2/firebase-app.js');
        importScripts('https://www.gstatic.com/firebasejs/9.0.2/firebase-messaging.js');
   
        // Initialize the Firebase app in the service worker by passing the generated config
        var firebaseConfig = {
              apiKey: "",
              authDomain: "",
              projectId: "",
              storageBucket: "",
              messagingSenderId: "",
              appId: "",
              measurementId: ""
          };
   
          firebase.initializeApp(firebaseConfig);
   
          // Retrieve firebase messaging
          const messaging = firebase.messaging();
   
          messaging.onBackgroundMessage(function (payload) {
          console.log('Received background message ', payload);
   
          const notificationTitle = payload.notification.title;
          const notificationOptions = {
              body: payload.notification.body,
          };
   
          self.registration.showNotification(notificationTitle,
              notificationOptions);
          });
   

3. Send notification via POSTMAN:

         {
            "message": {
              "token": "FCM TOKEN",
              "notification": {
                "body": "Body of Your Notification in data",
                "title": "Title of Your Notification in data"
              }
            }
          }
   

This procedure will replicate duplicate background notification.