Trying to do some sun rays/god rays/volumetric light shafts.
Following this approach.
Note. You need a modern browser that supports WebGL for this to run the way it is intended.
For example. Google Chrome 9+ or Firefox 4+.
(If you are already using one of those browsers and it's still not running, it's possible that you
have old blacklisted GPU drivers. Try updating the drivers for your graphic card.
Or try to set a '--ignore-gpu-blacklist' switch for the browser.)