Is there any short explanation how this works under the hood?<p>Does the browser maintain an open connection (like a Websocket) for each subscription, or there are some brokers, or if it can use OS facilities (like GCM&#x2F;APN on mobile) when available, etc etc.<p>In particular, I&#x27;m curious of privacy implications. When I subscribe - what site knows of me (say, if that&#x27;s a direct connections, I&#x27;m not sure I want to tell every site out there when I&#x27;m online), or if any third parties are involved - what they know and do (say, what&#x27;s about sender and receiver authentication)?<p>From what I saw (but really not sure I got it right), it seems that I have to trust browser vendor and maintain a live connection to some Mozilla server, that&#x27;d listen for events (POSTs from sites) and aggregate them for me. But I&#x27;m not sure I understood it correctly.<p>I&#x27;ll surely investigate this properly, but reading standards is tough, and end-user introductions written by marketing people are virtually useless. So I wonder if there&#x27;s a short reading to get the overall picture quick, but still see all the important details.