You can get a prototype WebCL extension for Firefox 10 from Nokia Research here: http://webcl.nokiaresearch.com/
The concept is similar to WebGL. While WebGL provides OpenGL bindings to Javascript, WebCL provides OpenCL bindings.
I then tried the Particles demo linked from there, and it was pretty impressive. FPS using Javascript was around 7FPS while it shot up to about 60FPS in the WebCL version (laptop using AMD A8-3500M on Windows 7 x64).
