This is the first beta from Mozilla to include support for <video> and the <audio> elements. This beta includes support for the OGG Theora and OGG Vorbis formats on all platforms.
It’s going to be easier to use this format if millions of users will be able to play it without adding additional plugins. This is really a major milestone for open standards on the web. The pressure on patented formats like the whole MPEG4 family will increase.
More juicy details about FF beta 1 on Firefox 3.1 beta 1 – an overview of features for web developers.