It's not difficult, they just don't want to support it because it isn't used. And because it added to download size. The two reasons are download size and lack of use and increase attack surface for security vulnerabilities. The three reasons are lack of use and vulnerabilities and download size and it's too complicated. The four problems... No, amongst the many problems with MNG are such diverse reasons as download size, lack of use... Oh bugger, I'll reply again.

Although there are many diverse reasons that Mozilla developers give for not allowing MNG support to be added in Gecko, they propose it can be supported by an imagelib extension, and that an image type finder (similar to the plugin finder) could be used to find the appropriate imagelib extension when a user goes to a page that has a MNG image on it. <<https://bugzilla.mozilla.…how_bug.cgi?id=18574#c672>> The same idea could be used to add support for JPEG 2000 <<https://bugzilla.mozilla.org/show_bug.cgi?id=36351>> and TIFF <<https://bugzilla.mozilla.…rg/show_bug.cgi?id=160261>>