[Late] Build Firefox on Windows 8.1

To Build firefox on Windows 8.1, there are a few steps needed.

1. Install Visual Studio (2010 - 2013)
2. Download and install mozilla-build bundle
3. Runs start-shell-msvc2013.bat in C:\mozilla-build and It will give you a CLI environment for compilation using Visual Studio 2013.
4. Cd to the root of the source folder that is downloaded from Mozilla repository

Build it by running:

./mach build

Finally, Runs it:

./mach run

Thanks to Mozilla, the whole building process is pretty smooth without any configurations. :)

Done!