Source Code: This page lists the various ways you can access the Mozilla source code, including downloading the whole thing via FTP or CVS, or various other views of the source tree as a whole.
Binaries: This page contains pointers to precompiled executable versions.
Documentation: Documentation relating to the source code goes here, including FAQs and build instructions and so on.
License Terms: This page describes, in many levels of detail, the terms of the license terms under which the Mozilla code is distributed (the ``NPL'' and ``MPL'' licenses.)
Bugs: The Mozilla Bug Center is where developers can report bugs in the Mozilla source releases, and browse an online database of already-reported bugs.