Separate browser wouldn't do a damn thing, because the MAC address of the computer and sometimes IP address would be the same. That's how they're doing it.
I have never heard of a browser connecting and transmitting the MAC address somewhere outside of the local network. As far as I know that can't happen.
Well Primfeed is alive and kicking, it also sorted out its issues in the beginnings and was even mentioned in one of the official newsletters by Linden Lab lately.