The Mozilla HTML5 Web App marketplace is alive and you can find a ton of information about it here:
http://hacks.mozilla.org/2012/02/mozillamarketplace-open-for-app-submissions/
Construct 2 works very well on Mozilla Firefox. I haven't looked deeply at this, but if Chrome and Windows 8 have exporters, then it seems like there should be a Mozilla one as well.
PS: I don't remember if I said, but the Windows 8 exporter works just great for the Windows 8 Consumer Preview.