If you’re on high speed Internet, you’re also going to want to consider this little speed-up trick. By default Firefox is set to only download pages to your browser with four simultaneous connections. This is alright if you’re on dial-up, but broadband can handle a lot more than that.
Again type about:config in your browser’s address bar.
On the config page, look for these three entries: network.http.pipelining, network.http.proxy.pipelining, and network.http.pipelining.maxrequests.
Change network.http.pipelining and network.http.proxy.pipelining to True.
Change network.http.pipelining.maxrequests to a higher number based on your net speed - somewhere between 10 and 30 ought to do it.
As a final step, right-click the screen and select New-> Integer. Name it nglayout.initialpaint.delay and set its value to “0″. This sets the amount of time the browser sits on its ass before acting.
See the original article at Forever Geek. And if you are using IE, bang your head against your desk five times and then check out this video for a solution just for you.
And finally, if that’s not enough - check out this nifty tool for tuning up Firefox. Appropriately named FireTune, the free application from Totalidea Software tunes up Firefox to work faster (very likely by implementing some of the above).