In this respect (and probably others) Mozilla is more like a ragtag army of rebels than a uniform-wearing platoon of soldiers. The blog is hosted on WordPress because the person who started it found it most convenient, and it never got migrated anywhere else. We also have hundreds of different github organizations and repos (despite also hosting our own "official" mercurial server), use lots of different communication tools, spread documentation over multiple wikis and bug trackers, etc.

But yes, this is an "official" blog from Mozilla employees on the graphics team, of which I too am a member.