The material applied to the sphere is created using a static PNG with a DisplacementMapFilter applied to it. The DisplacementMapFilter uses a BitmapData object that has had perlin noise applied to it to give the flame effect. A lot of other effects can be created this way as well. Things like rippling water or clouds. It’s just a matter of changing the original image and tweaking the settings of the filter and the noise.
You can get the source here. It’s really quite simple. The whole thing is under 200 lines of code.