"Maybe the most important new feature in this release,
at least for the open-source community, is the support for the
video and audio tags, which make possible to view movies in the
open video format Ogg Theora. These can be embedded in web pages
just like YouTube videos are, but without the need of Flash.
Besides, you can also directly download the video by right clicking
on it. Mozilla has put up on their homepage an example of how this
"Firefox 3.5 comes with support for open video formats - notice
that you can save the videos to your computer"