Firefox Alpha 3 (code name Bon Echo) has been released to achieve the goal of having a feature complete build at the alpha level. Since this alpha is incremental compared to Alpha 2.
Yes, no big deal. However it adds at least a couple of advantages over in-house developed Mozilla installer. First, it is a whole project dedicated to installing software so it delivers a higher level of flexibility and compatibility, including the option to download optional components/patches from the web at setup time, multiple languages in a single installer, patching and automated installation. Plus, NSIS is widely used by a number of other software makers so the interface may be already familiar for users. The installer is also a tad smaller (around 100KB).
Firefox, Bon Echo, Alpha