Last time I checked, Gecko and all the other browsers still had a long way to go before being fully HTML5 compliant. Chunks of the File API, postMessage, and a

Last time I checked, Gecko and all the other browsers still had a long way to go before being fully HTML5 compliant. Chunks of the File API, postMessage, and a variety of other specs are incomplete and underdocumented. Sites like caniuse.com vastly overestimate what has been sufficiently implemented.