How to pass data between users and different browsers in React?

I am learning React and I’m making an app to better learn.
I created an app with Nodejs backend, Postgres DB and React frontend. I have different users and this is the case of what I need to do:

USER 1: Logs in mozilla and clicks a button on a page.
USER 2: Logs in firefox and sees a new button has appeared, because user in mozilla clicked it. Now he clicks this new button.
USER 1: Because USER 2 clicked new button, USER 1 sees something new displayed.

I am running it locally.