You need to use a browser supporting WebGL for the demo to work, so it only includes Chrome, Firefox and Safari.
And you also need to have WebGL enabled on those browser. See here for more details about how to enable it.
The full source code is available here:
Here are some .json file I created with Inventor to play with: download them locally and drop them in the upper zone...
Z + Mouse to Zoom
P + Mouse to Pan
R + Mouse to Rotate