Ever since I started using Firefox I've been discovering new and awesome ways it can be tweaked. It started with speeding up Firefox and has progressed into everything from where my tabs are placed to how selecting text happens (see the layout.word_select options below).
Below is a list of all the options I have added/modified using the about:config function of Firefox (simply type about:config in the address bar). I have decided to save space and time by opting out of writing descriptions for each option. I've linked each option to it's respective page on MozillaZine. If you'd like a more layman explanation of each option, you can search Google or check out this article. If an option doesn't exist, create it.
Value Preference Name --------------------------------------------------------- 0 nglayout.initialpaint.delay 1000000 content.notify.interval true content.notify.ontimer true content.interrupt.parsing 2000000 content.max.tokenizing.time 3000000 content.switch.threshold false layout.word_select.eat_space_to_next_word false layout.word_select.stop_at_punctuation 32 network.http.max-connections 8 network.http.max-connections-per-server 8 network.http.max-persistent-connections-per-server 0 network.http.request.max-start-delay true network.http.pipelining 30 network.http.pipelining.maxrequests false browser.cache.memory.enable* 0 browser.sessionhistory.max_total_viewers true config.trim_on_minimize
I will add tweaks to this list as I discover them, mainly as a reference for myself. Some of the options require other options to be enabled, so if you're not going to use all of the tweaks listed here, make sure you do your research before complaining that its not working.
*UPDATE: See my post here about browser.cache.memory.enable. The short version: don't use it!