They might be able to see if the data indicates the network has been though NAT (network address translation) twice, but that would look just like someone who has plugged their own wifi box into the modem

There’s always NAT. You get one IP address, your router/wifi shares the network using NAT

But ISPs aren’t looking for NAT, since everyone with wifi is using it

Were Firefox to go bad, we would use a non-bad fork off Firefox. It’s open source.

Do you mean that you don’t like the way they prefer to defend individuals against corporations rather than the other way around, or the way they don’t help people defend themselves against lawful and reasonable government action?