Everyone I know who uses FireFox also uses the web developer extension. That extension has many wonderful features. One I’ve just started using recently is the ability to hack CSS on the fly. This is really handy when you’re trying to read a lengthy online work that is formatted without any styling or with bad styling you want to work around.
Case in point, eskimo.com has some great tutorials on C programming. But the formatting is straight out of 1996. By simply defining a paragraph and heading style, you can turn this into this.