You can select the plugins you want, or just install them all, it’s your choice.
over 3000 downloads in 24 hours, impressive
Customize websites With Firefox
The great advantage that Firefox has compared to for example IE is that it is far more customizable. I already talked about some of my favorite extensions, and Greasemonkey is another one. Greasemonkey allows you to install all kinds of useful user scripts so you can customize the web to your own needs (in a sense).
It is not even that hard to edit those scripts to your own needs, or create scripts of your own. This excellent site has a nice overview of things you can do with Greasemonkey, and more important, how to.