MP3 and H.264 should play fine on Firefox OS if the device vendor includes hardware support for it. The initial devices do support this as far as I know. Firef

MP3 and H.264 should play fine on Firefox OS if the device vendor includes hardware support for it. The initial devices do support this as far as I know. Firefox for Android for some devices also supports MP3 and H.264 now. Desktop support is in progress with Windows and Linux being the furthest along.