[grun]

Great questions!

> How does the website possibly detect that I'm on a cellular network when I'm a) use Firefox (which doesn't implement the NetworkInformation API) and b) use a VPN to either a data center or my home server?

Yep. An IP lookup is also done to see which AS the user is on. Eg an AWS IP vs a T-Mobile IP.

We also do this to detect when people tether, as when tethering Chrome will report a Wi-Fi connection via the NetworkInforamtion API but it's Wi-Fi on top of an underlying cellular connection.

> There's also the massive privacy issue: other people will know what websites you visit by simply using the P2P system

All cached data is both fragmented and encrypted. When a node sends data to another peer, it's an encrypted fragment of a file and the sender doesn't know 1) what data it's sending nor 2) which website that data is being sent for.