Roadmap: The Mozilla Development Roadmap describes where the browser code has been, where it is going, and why. It outlines design principles, and enumerates design decisions and major work items as they happen. Read this document to learn the goals we're driving toward, and to get a feel for the terrain.
Module Owners: The Module Owners document lists the points-of-contact for the various source code directories that comprise Mozilla: that is, the people responsible for the code that mozilla.org distributes. Talk to these people when you want to change the code for which they are responsible.
Blue Sky: The Blue Sky column is a pulpit whereby we (or rather, the editors of that column) advocate projects that nobody has yet started working on. If you are itching to work on something new, this is the place to go seeking inspiration. Much of the content of this column comes from and is inspired by the mozilla-wishlist forum.
Projects: This page lists links to active Mozilla projects. These pages explain what's going on in the codebase, what work it entails, and who is doing the work.
Status: The status column, written by Chris Nelson of MozillaZine fame, collects weekly project status updates from module owners.
Tools: This page lists the various development tools that we operate and/or maintain here at mozilla.org.