The problem with the make included with MozillaBuild is that it doesn’t take advantage of multiple processor cores on Windows. So even if you have a crazy-powerful 8-core machine, when you just use the vanilla “make -f client.mk” command, you’re only going to be using one of your cores. Enter pymake. Pymake is a Mozilla-maintained mostly-compatible implementation of make in Python. The advantage? On Windows, we can finally use all of our cores.
http://mikeconley.ca/blog/2011/11/30/build-thunderbird-faster-on-windows/
Source: mikeconley.ca
