WebCL implementations for Firefox and Chromium exist for 2 years. But they have not been included in any alpha, beta or canary release. Browser developers don't seem to care about WebCL, but they do care about WebGL, which is strange.

Samsung made it work in Tizen, but sadly, it is not very widespread OS. https://www.youtube.com/watch?v=TurCVdaUTMY