Since May, we've been running our unittest suite twice for each checkin: once for the current reference counting build + test job, and once for the packaged unittests. Current way of running tests Our end goal is to run unittests on our optimized and debug builds. We would stop doing our current reference counting builds, since the debug builds also have reference counting enabled. New way of running tests To get there requires a few intermediate steps: At some point we're also going to be changing how we run mochitests, by splitting the tests up according to which directory they're in, and then running each of the subset of tests in parallel on different machines (bug 452861).