The mozilla source code for all projects (Firefox, Thunderbird) is combined into a single tree. This tree contains all the source code for all the projects in the mozilla family and all the code required to build each project on the platforms each project supports (Linux, Windows, Mac OS, etc).
Getting the Source Code
You can download a compressed file of a snapshot of the sources or you can check out the current sources from cvs. Mozilla Source Code Via CVS
The Source Code Directory Structure
The top level directories in the mozilla cvs repository are:
Contains 2 readme files: mozilla/README.build & mozilla/README.os2
Provides the hooks to enable support for hearing and sight impaired users.
Seemingly empty directory.
An empty directory.
Contains the source code for the Mozilla browser. This code is shared between all ports (Mozilla, Firefox, etc) and platforms (Linux,Windows,Mac OS, etc).
The files needed to create packages (autoconf,rpm,deb,unix,wince,mac,etc).
From the README in calandar/ :
resources/ content/ - This directory contains all the XUL and JS files needed for the calendar. /test - Test files for the calendar. These are not needed to run it. locale/ - Where the text for the calendar ends up, as well as definitions for dates and date formats. en-US/ skin/ - Graphics and CSS files defining the look of the calendar. modern/ ca-event-dialog/ - Graphics and CSS files for the dialog which adds and edits events. classic/ ca-event-dialog/ - Graphics and CSS files for the dialog which adds and edits events. libxpical/ - An XPCOM interface to the libical library. This is needed to retreive and write calendar information to a file.