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network.http.pipelining user_set boolean true
network.http.pipelining.aggressive user_set boolean true
network.http.pipelining.ssl user_set boolean true
network.http.proxy.pipelining user_set boolean true

Increase

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Connections

As it turns out, this first setting is artifically low on the presumption you'll be using a public proxy
on the Internet and that it's "bad etiquette" to send such a server too many connections.
Being that I'm not going to kick myself off my own proxy server, I went ahead and changed this.

The second setting just reflects what's already been configured in ATS.

network.http.proxy.max-persistent-connections-per-proxy user_set integer 256
network.http.max-persistent-connections-per-server user_set integer 32 

Experimental

This setting I've had no end of annoyance finding documentation for.  I believe it has to do with predictive HTTP parsing, and the default is pretty low.

network.http.speculative-parallel-limit user_set integer 256

That's it. Go ahead and restart your browser just to be safe, then enjoy your increased surfing speeds.