Google Poop — Mr Doob Fix Best
To trigger the falling effect, you often have to actually interact with the page or type into the search bar. If the elements are static, try resizing your browser window to "wake up" the physics engine.
Similar to Gravity, but elements float around in zero-G, reacting to your mouse movements. How to "Fix" or Use Them If you are trying to find these to play with them today: google poop mr doob fix