Firefox 3.5 FAQ – Nicely-written, and brought my attention to Fashion Your Firefox, a website which recommends add-ons for your installation.
Q: How can I customize Firefox 3.5?
A: Firefox is the most customizable browser on the planet. With a growing library of more than 6,000 free Firefox add-ons, little extras you download and install for a browser that works your way. Manage online auctions, upload digital photos, see the weather forecast in a glance and listen to music all within Firefox. If you’re not sure where to begin, try Fashion Your Firefox—a handy Web application that recommends add-ons based on your interests. Get it at: http://www.fashionyourfirefox.com