Originally Posted by TheDoc

Here are some other handy ones, some of these may only work in ff3.

browser.urlbar.clickSelectsAll = True
toolkit.scrollbox.scrollIncrement = 75

Enable spell check in text fields
layout.spellcheckDefault = 2

To speed up the browser
network.http.max-connections = 96
network.http.max-connections-per-server = 32
network.http.max-persistent-connections-per-server = 8
network.http.pipelining = true
network.http.proxy.pipelining = true
network.http.pipelining.maxrequests = 8
network.http.pipelining.ssl = true
network.http.proxy.pipelining = true

Make animations only loop once to stop annoying ads, sigs, and avatars.
image.animation_mode = once

network.prefetch-next = false

To show more tabs on single window
browser.tabs.tabMinWidth = 75

Stop Displaying Website Icon (Favicon) in Address bar & On Tab
browser.chrome.site_icons = false

Scroll webpage in One Go
mousewheel.withaltkey.action = 1