As you can see lots of new feature come in MDN. Here first you have to play with MDN . Now you have make a create a documentation with screen shots so new contributor can get full ideas how to hack in MDN.

This documentation includes

1. Proper description with of each steps with screen shots

2 If possible make a screen cast also.

Important links: http://developer.mozilla.org/

this is old guide https://docs.google.com/file/d/0B1qJEkrT0AW8cDdrYUc1cWR3R05NUlgwT285aHM5bHJXdTJF/edit

You have to make new one on the basis of old. It needs updated content, new screenshots and the github login information etc added.