From Firefox Tuning – MozillaZine Forums…
Type “about:config” in your FireFox address bar, then make the following changes:
network.http.pipelining = true
network.http.maxrequests = 8
network.http.proxy.pipelining = true
browser.turbo.enabled = true
Note that the above changes should result in a visible speedup (they did for me), but you may experience some display glitches or other issues on a few sites. If you have too many problems, revert the above parameters to their original settings.