It works out to 'hacking firefox' :)

Anyway, here are a few techniques and widgets I've used to trick out my firefox browser. Most of these tricks work on both the old and the new firefox.

First: split browsing. This is an idea I had entirely on my own, where on one firefox window, it shows two pages right next to each other. You can make the pages be side-by-side, above-and-below, etc, and there is no limit to how many extra windows you can have open like this. Also, every split window has it's own tabs, address bar, 'forward/back', 'stop' and 'refresh' icon.
This hack is particularly useful for doing research. It means you can have a web page open and at the same time check all the sources to see if it's legitimate or if you're wasting your time.
https://addons.mozilla.org/en-US/firefox/addon/4287

Second: speeding up the loading of objects in firefox. I should note here, normally you only want to do this if you have a moderately fast connection- DSL or greater- but it will work with any connection and speed things up at least a little bit.
In the address bar in firefox (open up a new tab), type 'about:config' and press enter. You'll get a little warning that comes up and says "be careful! this might void your warranty!". When this happens, click 'continue' (firefox 2) or 'i'll be careful' (firefox 3), and it will come up with a very big list of things that are what make firefox work. In the search bar (at the top of the screen, under the address bar), type "pipelining". It should come up with about 4 objects, 3 of them listed as 'boolean' (meaning they are true or false statements made to the computer) and one is listed as an 'integer' (a whole number). The first thing you'll want to do here is double click all the boolean statements to turn them from 'false' to 'true'. This means that your computer will dedicate network bandwidth to firefox only. The second thing you want to do is double click the 'integer' in that list and set it to some very high number- the default is something like 4, if I recall correctly. Mine is currently set to 500. What this variable does is increases the number of requests that your browser makes of a web page at a single time. More is generally better, hence mine being set at 500.

Lastly, right click somewhere on the browser, select 'new'-'integer' and name it "nglayout.initialpaint.delay", and set the value to '0'. What this does is it turns the delay between firefox getting info and firefox showing info down to zero. In laymans terms, this means it shows things faster.

There are many more little things that can be done to speed firefox up, but this is the basic set of instructions you'll see anywhere you look for how to speed firefox up.

Also see: (Admin Addition)
Firefox IS Better for more hints and useful add-ons.