You have likely heard it a million times already, Firefox 3 is a very nice improvement over version 2, especially in the performance department. And while many still prefer to stick to their own improved versions of Opera and Safari (sorry IE, you are a disgrace right now), Firefox is by far the most used alternative browser. I believe that comes in part thanks to its flexibility for customization and the myriad of useful add-ons you can get for it.
I can’t stress enough the add-on part. From webmaster tools, to simple functionality tweaks and social networking integration. My following tips, however, lay on the side of about:config tweaks (that is, you have to manually apply these yourself in the settings registry by running the about:config command on the address bar). So here we go: