I wouldn't set them
too high or you'll hammer the server. Here's what I have:
network.http.max-connections - 48 (default 24)
network.http.max-connections-per-server - 24 (default 8)
network.http.max-persistent-connections-per-proxy - 12 (default 4)
network.http.max-persistent-connections-per-server - 6 (default 2)
network.http.pipelining - true
network.http.pipelining.maxrequests - 8 (default 4)
network.http.proxy.pipelining - true
And for a little more rendering speed, right-click anywhere and select New > Integer. Name it "nglayout.initialpaint.delay" and set the value to 0. This changes the amount of time the browser waits before it acts on information it recieves