some good tips can be found here:

1. Type “about:config” into the address bar and hit return. Scroll down and look for the following entries:

   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 recieves.

If you’re using a broadband connection you’ll load pages MUCH faster now!

The nglayout part sounded fishy to me, but after a check at mozilla.org I trieded it and it seem to improve performance a little bit. Actually, the last step will not make your pages load faster but will try to display them anyway, which makes you think everything is loading faster…