Trying to understand how FCM works with Chrome Extensions to debug a push notification issue

[Anchal Nigam]

I am using G-Suite Enterprise inside a corporate firewall. 

The Checkers Plus for Google Calendar extension uses FCM to enable the extension in my browser to get push notification/updates when my Google Calendar is updated.

Right now the extension does not seem to be getting the push notifications. I read https://firebase.google.com/docs/cloud-messaging/concept-options#messaging-ports-and-your-firewall and understand that we need to allow certain ports in our FW.

My question is, would I need to allow those ports in our corporate network or will the extension provider need to open those ports on their firewall?

I'm unsure of how the data-flow goes. After the extension registers for push notifications, when there is a new push notification, what happens:

• The push notifications go to my browser
• The push notification will go to the extension's back-end server and then the extension's back-end will push it to my browser

I'm just trying to understand the data-flow so I know where the ports need to be opened.