Follow the [http://developer.mozilla.org/en/docs/Build_Documentation normal build instructions] and [http://developer.mozilla.org/en/docs/Mozilla_Source_Code_Via_CVS get the source from CVS], except when checking out <code>client.mk</code>, use
Using <code>client.mk</code> to pull the rest of the tree is essential because only layout is branched; everything other than layout is pulled by date.