Made the example working of Firefox (added unprefixed CSS properties for 3d transformation)

The current example uses `webkit-` prefix CSS property only, it means it doesn't work in any modern browser that uses standard and unprefixed property. Fixing that makes the example working on Firefox too – tested –, and potentially to any modern browsers that uses unprefixed properties.

This PR also trying to simplify a bit the JS code, and improve the overall performances.