MDN documentation is coordinated and driven (sometimes called "shepherded") by per-topic leads. Any topic may have a curator or a driver or both. A Topic Curator is a member of the Mozilla MDN staff team who are responsible for looking after content in broad areas of MDN. A Topic Driver is someone not on the Mozilla MDN staff team (though they might be a Mozilla employee), who keeps up with changes in their topic area, and helps ensure that the content for that area is accurate and up-to-date. Note that curators and drivers do not necessarily write all the content for a topic!
We can always use for help! If there's a topic that you're interested in, please jump in and contribute. If there's a topic area that not listed, please add it! If you want to discuss what's needed (often a good idea), you can post on the MDN discussion forum, or pop into #mdn on IRC. (Staff are most likely to be active on IRC during business hours in Europe or North America.) Address any questions to Chris Mills (the content lead).
See Topic driver role for details about how to go about becoming a topic driver, and what the role entails.