Added a note on how to solve the Chrome issue:

In order to support chrome FCM registration api needs to be activated in the google console:

• https://firebase.google.com/docs/cloud-messaging/js/client#add_firebase_to_your_javascript_project
• https://console.cloud.google.com/apis/library/fcmregistrations.googleapis.com
  
  

Added is subscribed info.

Some problems were identified with certain instances of Chrome web browser.

Firefox has proven to be more stable and at the moment no issues with Firefox were identified.

Added Unsubscribe and Subscribe again options.

This is because after subscribing for the first time, even with the app closed but the Browser opened, we will keep receiving notifications. 

For the moment the way to deal with this will be to unsubscribe notifications.