Regarding APNG, Mozilla developers proposed it for inclusion in libpng, but got laughed out of the PNG group. The sole maintainer of the libpng APNG patches decided to stop working on it last year. Browser support for APNG is limited to Opera and Mozilla based browsers (except Debian Iceweasel and other Linux distros that build against system libpng instead of the Mozilla internal one).
Application support for MNG seems more widespread than APNG. Browser support is worse, although contrary to what has been claimed, Konqueror is a modern browser which supports MNG.
You do know what Mozilla is, right? The MNG farce extends back long before Firefox existed.
Yes, I know what Mozilla is, but I assumed he was only talking about Firefox, since back in the Netscape days, they could have easily had a license for GIF, and not enough people used vanilla Mozilla back in the day to make it a worthwhile target to sue. Plus, GIF was a lot more widespread back then than JPEG2000 is now, making it more important to support.
Or maybe the guy who developed JPEG2000 drove over one of the Mozilla developer's cats, who knows?