The demo currently uses a 64×64 mesh grid to represent an ocean surface tile and every surface update requires the computation of 5 64×64 point 2DFFTs (heights, x/z displacements & normals). Performance wise, an Intel i5-2500K based machine with a Radeon HD6950 achieves 53FPS in Chrome and a Samsung Galaxy S3 running experimental WebGL in Chrome gets around 10FPS, which isn’t really fast enough to be considered interactive but I’m still impressed that it worked without any additional effort on my part. Performance could be improved considerably by moving parts of the ocean simulation (notably the FFT) onto the GPU.
Access the demo here.
The sections on the right hand side of the page let you control the ocean surface parameters and adjust the inputs to the surface shader. Enable or disable the mouse based camera by pressing ‘M’ and move around the scene using the WSAD keys.
 Tessendorf, Jerry. “Simulating ocean water.” Simulating Nature: Realistic and Interactive Techniques. SIGGRAPH (2001).