I'm not sure what you mean by "MPEG Audio". AAC is standardized as a part of MPEG-2 and MPEG-4 specification. This extension can play any of the supported codecs and formats listed here https://developer.mozilla.org/en-US/docs/Web/HTML/Supported_media_formats.

If your stream uses AC-3 audio by any chance, it is not supported by Firefox. AC-3 is also not part of MPEG spec. You can also read about the support for AC-3 on https://github.com/video-dev/hls.js/pull/1102. This is not yet merged, and as it seems, it can only be supported on Edge and Safari, since they have AC-3 support.

MP2 is not supported at all.