1.Type "about:config" into the address bar and hit return. Scroll down and look for the following entries:Link (Thanks, daede!)
network.http.pipelining network.http.proxy.pipelining network.http.pipelining.maxrequests
Normally the browser will make one request to a web page at a time. When you enable pipelining it will make several at once, which really speeds up page loading.
2. Alter the entries as follows:
Set "network.http.pipelining" to "true"
Set "network.http.proxy.pipelining" to "true"
Set "network.http.pipelining.maxrequests" to some number like 30. This means it will make 30 requests at once.
3. Lastly right-click anywhere and select New-> Integer. Name it "nglayout.initialpaint.delay" and set its value to "0". This value is the amount of time the browser waits before it acts on information it receives.
If you're using a broadband connection you'll load pages MUCH faster now!
Update: Ole sez, "Enabling pipelining in Firefox can speed up complex page retrievals, as you note, but it can also break Flash. This is a Macromedia thing not a Firefox thing but that’s why the app defaults to pipelining disabled."