compiling the sources
If you have installed everything properly and downloaded the current source tree either using the cvs server at cvs.mozilla.org or in tarball form and applied the patches, you can begin to compile the sources.
Now you must also have some command file that sets up the environment variables and adjusts the PATH and BEGINLIBPATH (for example, it may look like this: warpzilla.cmd).
You can either use emx/gcc or VisualAge for C++. An environment setting in your setup script warpzilla.cmd will determine which compiler the make utility uses.
The most upto date build instructions known are way over on the East coast of America: Joan Touzet's page.
Tip: Help is often available in the newsgroup.
You may also look on John Fairhurst's NGLayout web page.
autoconf build
The main mozilla source tree has moved to an autoconf build system and has gotten rid of all makefiles (except maybe in nsprpub) so the system is in continuing flux these days and may even require some additional tools; Henry would be pleased to receive help moving the conversion along.