I just tried the viewer and you're right, the keyboard doesn't work under Ubuntu 12.04 with Firefox (but it works under Windows 7/8 and Mac OS X).
It seems like the applet is unable to gain the keyboard focus, because no colored border appears around the 3D view when you click in it or press the tab key. Similarly, the online version is able to gain the focus only when you click in the catalog?!?
Can anybody try with some other browser under Linux?
I suggested a feature request for explaining the key/mouse functions in the viewer
The HTML file proposed with the viewer contains the minimum script able to run the viewer. In the real world, like you did in your nice example, this script should be inserted in a web page with some web site navigation, copyright notices and/or why not a minimal user guide that could cite some information from the help. Anyway, thanks for posting the request and the ideas you gave. 
By the way, the coming version will fix an other bug I found in the viewer that prevented to use the the home and end keys to move up or down the visitor's point of view.
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Emmanuel Puybaret, Sweet Home 3D creator
