from ignightmare on ign forums:
1) type in 'about:config' in your address bar
2) type in 'pip' in the top filter bar
3) Set 'network.http. pipeling' to TRUE (right click > toggle)
4) Set 'network.http. proxy. pipelining' to TRUE (right click > toggle)
5) Set 'network.http. pipelinging. maxrequests' to a number. (try numbers between 5 and 50 to see what works the best for you)
6) Right click > New > Integer
7) Type in 'nglayout.initialpaint.delay'
8) Type in '0'
video:
http://www.metacafe.com/watch/322730/how_to_make_mozilla_firefox_run_much_faster/