"Other significant changes will arrive in Firefox
3.1...Another is the built-in ability to play music encoded with
the Ogg Vorbis format and video encoded with the Ogg Theora format.
These formats, while not nearly as widely used or as supported as
rivals such as MP3, are free from proprietary constraints such as
patents, Shaver said, and therefore can be added to an open-source
project such as Firefox."