To be fair, it's incredibly CPU-heavy. It uses an iterative approach to calculate the forces exerted on the grid, so for each frame it calculates the force exerted on each node a set number of times. (See http://en.wikipedia.org/wiki/Verlet_integration)
However, this shouldn't be so heavy that the Firefox JS engine struggles with it...
However, this shouldn't be so heavy that the Firefox JS engine struggles with it...