It's hard to imagine it would be better than Disqus or Stack Exchange. Why not go to a commercial vendor with experience to solve this problem? What expertise or developed software does Mozilla have? Are they very good at managing this kind of development? At least the companies in this market are ongoing enterprises that have shaken out the bugs in their process. Mozilla, as we've seen recently, is a mess.
I don't think this is the problem to solve. What both news organizations need to do, have needed to do since the web took off 20 years ago, is find a way to get the expertise of their sources to flow directly through their publications. In the mid-late 90s this could have quickly and easily been accomplished by hosting a reliable blogging platform. Then, as your reporters do their jobs, they would have a much bigger array of expertise to tap, better organized, and the volume and quality of their work would go up. But that opportunity was missed, as Blogger and then WordPress and Tumblr grew to fill the need.
No matter! The opportunity is still there. Facebook and Twitter haven't managed to capture the flow of expertise yet. The Times & Post would be very lucky if they turn out to have two years to spend on research with Mozilla. Maybe they will be that lucky, they have been so far. But I don't like the bet if I'm Bezos or Sulzberger.
I recommend: Get a list of the sites the editorial people at the Times and the Post read. I'd try to automate the process so the list is huge and inclusive. Aggregate them into a river. There's your community of bloggers. Publish the river on your home page. Read what they write, and share it with your readers. This will immediately have huge influence on the both the blogosphere that you include and the ones you don't. Include your competitors. (This is the same philosophy that Yahoo used to grow their news presence in the early days of RSS, people would happily go to Yahoo to find out what's new on CNN or MSNBC. Basic web principle, people return to places that send them away.)
Constantly recalc the list of feeds that make up your rivers, and segment them over time into business sports, international, theater, food, politics, tech, the usual categories.
You need to grow. We need you to grow. Time is really of the essence. The method most people use to get news is broken (if it's important it will find me). What finds us via Twitter is mostly crap. We need to get good at find lots of great relevant writing by experts. That's what we're not doing. Building a better commenting system, which is doubtful, really doesn't help us very much, esp since it probably won't be better than the commercial systems that are available today.