-Open Firefox and on the address bar write "about :config" and hit enter

-find the string network.http.pipelining
-double click and change the value to true

-find the string network.http.pipelining.maxrequests
-double click and change the value to 34

-find the string browser.turbo.enabled
-double click and change the value to true

-Now close and restart and enjoy the new
blazing speed of Firefox.

Or try the FasterFox extension.