FTP.
You can download the source from our FTP server. Details are on the Download page. Source drops to the FTP server occur regularly, on a schedule which has not yet been decided (possibly weekly, possibly monthly.)
CVS.
You can check out the source using CVS. If you are doing active development, this is the preferred method, as it lets you get up-to-the minute changes. Details are on our CVS page.
LXR.
You can browse the source code online, through a massively-hyperlinked source code browser that lets you cross-reference function and variable names. We plan to have a version of this up and running here at mozilla.org soon, and have it kept up-to-date with the latest and greatest code that is checked in to our main CVS repository.
For now, you can check out the LXR pages set up by the fine folks at mi.org.
Bonsai.
Bonsai is tree control (get it?) It is our our home-grown web-based tool for watching the up-to-the-minute goings-on in our CVS repository (viewing checkins and log messages, reading diffs, etc.) Check out the Bonsai page for details.
Tinderbox.
Tinderbox is for knowing when the tree is in flames. It is our our home-grown web-based tool for watching the progress of the continuous builds that we run on multiple platforms. It is how we are able to tell when a checkin has broken the build on some platform, and how we know which person needs to be viciously flogged. See the Tinderbox page for more.