From the start I closely followed two websites. The [http://developer.mozilla.org/en/docs/Build_Documentation#Build_Requirements| Mozilla build documentation ] and [http://cs.senecac.on.ca/%7Edavid.humphrey/writing/firefox-win32-build.html| David Humprey's guide to building Firefox ]. The following is the software needed to build Firefox on a Windows XP SP2 computer: '''7-Zip'''  This software is used to unpack the zip archive from the Mozilla FTP. If you are using cvs to download the Firefox source then you shouldn't need this.  '''Cygwin''' From what I can tell, this software emulates a Unix shell and in doing so downloads many commands and tools you need to compile Firefox. Once you download Cygwin follow the steps for installation. I used Unix shell endings and I also checked the following options.  * patchutils (under Interpreters). * perl (under Interpreters). * zip, unzip (under Archive).  Don't check Make unless it's version 3.80. '''Make 3.80''' I am putting this seperate because I had to download the Make software seperatly as I coulnd't find it in the Cywin tools. From what I can tell this utility does the actually building of Firefox.  '''Visual Studio 2003 or Visual Studio 2005''' Both Visual studios have tools that are neccesary to build Mozzila's Firefox. I personally had 2003 installed but switched to 2005 to try and fix a bug, which it didn't. Although you can get free tools out on the net, this is what I used and can say works. '''MozTools''' These tools created by Mozilla are used to build Firefox but I couldn't tell exsactly what they do.