socket.io falls back to long polling, so you have to be careful when trying to produce benchmarks based only on websockets. I didn't see this in the server code so I assume the default transports were used.

io.configure(ENV, function(){ io.set('transports', ['websocket']); });

more here: https://github.com/LearnBoost/Socket.IO/wiki/Configuring-Soc...

Also, Firefox version would be nice to know.