Straight to the steps;

Before you do this, be sure that you know what you are doing.

1. Type "about:config" without quotes on the adress bar and hit enter. If you are using Firefox 3, click on the "I'll be careful, I promise!" button. And Promise you'll be careful.
2. Next, on the filter, search for:

"network.http.pipelining", double click it, and change the value to 'true'
"network.http.proxy.pipelining", double click it and change its value to 'true'
then set "network.http.pipelining.maxrequests" to some number like 40. Now it will make 40 requests at once.

3. Now right click anywhere inside the page and select new -> integer, and name it "nglayout.initialpaint.delay" and set the value to 0.

How it works? Normally the browser makes one request to a web page at a time. When you enable pipelining it makes several requests at once, which really helps pages load much faster.