Most of the times I go through the web for finding tweaks for Firefox. I found these articles are very interesting and tweaks contained in these articles help me to improve the performance of Firefox.

1. About:config Entries - This is a reference to about:config entries which you can get basic understanding about those entries.
2. Ten Mysteries of about:config - about:config tweaks from Linux Journal.
3. Top Firefox 2 config tweaks - Written by Gina Trapani from lifehacker.com.
4. Firefox about:config Hacks and assorted tips - Some greate performance hacks for Firefox from Tech Yantra.
5. Make Firefox much faster about:config tutorial - Video tutorial from youtube.com and you can find more from related video list.
6. The secrets of about:config - Firefox Hacks from computerworld.
7. Firefox Tweak Guide - 12 page Firefox tweak guide from tweakguides.com.
8. Firefox Tweaks - Firefox tweaks for network connections and plugins.
9. Firefox performance tweaks - Another Firefox performance hacks.
10. Firefox memory tweaks - High usage of memory is some time a problem for Firefox users. This guide will help you to tweak the memory settings.

These guides some times contain same tweaks but I prefer you to read these and choose the best things.