Lectures may be viewed with complete interactivity on Windows 7/8 and Mac platforms. The lectures may also be viewed on Linux and mobile platforms without the browser interactivity provided by the Wolfram CDF Player.
The best browsers to view this material are the latest from Firefox and Safari. Chrome is OK, but navigation among pages doesn't work properly. Internet Explorer is the worst - avoid it.
Finally, clean your browser cache frequently - at least once daily. I continually update the material and you don't want to be reading old or even incorrect stuff.