- Run the one of the following batch files. In my case I am using visual studio 2010, so I lauched C:\mozilla-build\start-msvc10.bat.

- Download the source code for the release version you would like to build. In this case, I downloaded the source code for [ftp://ftp.mozilla.org/pub/mozilla.org/firefox/releases/4.0b9/source/ Firefox 4.0b9]