Changes

Every day, Mozilla developers write code that is merged into a common code repository (mozilla-central) and every day that code is compiled so as to create a pre-release version of Firefox based on this code for testing purposes, this is what we call a Nightly build. Once this code matures, it is merged into stabilization repositories (Beta and Dev Edition) where that code will be polished until we reach a level of quality that allows us to ship a new final version of Firefox to hundreds of millions of people. This development process used to ship a new version of Firefox every 4 to 5 weeks is called the Train Model.