Mozilla webdev here. I could be wrong, but given that the repo is still on Josh's github account (https://github.com/jdm/asknot) rather than the official Mozilla organization (https://github.com/mozilla/), my guess is that it's not "official".
I'm almost certain we know about it after the last time it hit Hacker News, and given the amount of people contributing to it (https://github.com/jdm/asknot/commits/master) there's at least some level of effort in making it better, but it probably doesn't have priority over official entry points for contribution, like http://www.mozilla.org/en-US/contribute/
I'm pretty sure this is an official Mozilla website. Plus, Josh Matthews is a Mozilla employee who, among other things, works on contributor engagement.
We're definitely blurring the bounds of official-ness. Everybody in the organization who has seen it is always enthusiastic, and nobody has asked me to remove the tabzilla branding.
