This document describes the process by which changes to Firefox source code become a general Firefox release. Firefox has hundreds of millions of users, so some care is in order.
Firefox uses a schedule-driven process, where releases take place at regular intervals. That means each release happens regardless of whether a given feature is ready, and releases are not delayed to wait for a feature to stabilize. The goal of the process is to provide regular improvements to users without disrupting longer term work.
Mozilla Firefox: Development Process：http://people.mozilla.com/~sayrer/2011/temp/process.html