We have no plans to use mozjpeg in Firefox, it will continue to use libjpeg-turbo. The decoder that comes with mozjpeg is unmodified from libjpeg-turbo, mozjpeg

We have no plans to use mozjpeg in Firefox, it will continue to use libjpeg-turbo. The decoder that comes with mozjpeg is unmodified from libjpeg-turbo, mozjpeg is focused on compression for those serving up images.