Originally Posted by BackToMine

Goto about:config
and set these settings:

browser.turbo.enabled = TRUE
browser.xul.error_pages.enabled = TRUE
nglayout.initialpaint.delay = 0
network.http.max-connections = 48
network.http.max-connections-per-server = 16

Excellent extensions:
PageRank & Alexa stats: http://www.quirk.co.za/searchstatus/
Web Developer tools: http://www.chrispederick.com/work/firefox/webdeveloper/
Opens all links in tabs etc: http://gemal.dk/mozilla/linky.html?ver=2.2.0