Attached to “Bug 18574 – (mng) restore support for MNG animation format and JNG image format” there was this new comment today: “I made Emscripten port of MNG. After 17 years from creating this issue.”
I found this comment to be VERY funny. But you probably need some context to understand it. Back in 1999, Mozilla added and then removed a library to support the MNG file format, which is like animated GIF, but using PNG technology instead of GIF so they are much smaller. There was much controversy. The flimsy rationalization was that the MNG library added too many bytes to the Mozilla download. But really it was about web standards.