Step 1: Type about:config into your location bar and hit Enter.
Step 2: In about:config, type network.http. A list will appear.
Step 3: Double-click inetwork.http.pipelining setting to change it to true.
Step 4: Double-click the network.http.proxy.pipelining setting to change it to true. (This'll only matter if you're behind a proxy)
Step 5: Double-click the network.http.pipelining.maxrequests setting, and in the text box that appears, type in 2, 4 or 6 and click OK. Yes, you can type in 100, but it would only be foolhardy.
In case your performance drops then you know some of the sites you are surfing have banned you for using more than the default pipelines. Just revert back to the previous settings and you should be ok. Fasterfox extension also does the same, but now since you have this that extension would be an excess baggage.