I've found the streaming of anything from build to be completely unreliable from the channel9 site. You can download the vids, but the download times are also horrendous. Seems to me this would be a great excuse for a company to use a torrent to spread their content. It's free anyway, why not use it and promote the legal use of a great technology?
Download and view it locally with the player of your choice: mplayer, xine, vlc, etc.
I can seek fine in mplayer.
The video won't play at all in my browser. FF24 on Gentoo.
You need silverlight.
Ugh. They did this with the feynman lectures, too.
Edit: Jumped the gun. Just downloaded it as an mp4 to watch in vlc.
Ubuntu/FF28 - I was able to watch the video in browser without issue. I most definitely do not have Silverlight.
The site offers alternative downloads of the video file. You should be able to watch these videos on linux with vlc or one of your favorite video players.