One of the great new features of Firefox 3.5 is the native support of the Ogg video format. If you don't know, Ogg is a Free and Open Source video format from Xiph.org.
What makes this feature so cool? Well, up until now we've all depended upon browser plugins to support video playback. One of the most common questions from new Ubuntu users is "How do I get the Flash video player installed?" It's not hard to get set up, but it's not installed by default. Other video formats such as .wmv, .mpg, and .avi also depend upon browser plugins.
Native support of Ogg means that any user of Firefox could view this video content without the need of extra plugins. Now Mozilla isn't just going rogue and creating support for non-standard features in Firefox. The W3C has proposed support for Ogg Theora be part of the HTML 5 Standard. So if all goes well, some day all standards compliant browsers will be able to play videos on their own.
After installing it, create a new Firefox profile to use with 3.5. You want to use a new profile so that you don't have any conflicts with currently installed plugins.
Assuming you called your new profile 'beta', you can start Firefox from your installation directory with:
Try Out an Ogg Video
Linux Journal posts their videos in both Flash and Ogg format, so go to http://www.linuxjournal.com/video and give it a try. The images on the page link to the Flash format. Instead, click the link to "Download in .ogv format".
Here's a link to today's Ogg video.