IE 10 only fails 7 tests compared to 200 for Firefox 5 out of a total of 10000 tests.
I don't use Opera, but according to this page http://en.wikipedia.org/wiki/ECMAScript Opera lags the other browser and fails 3000 tests. Does anyone have Opera and willing to run the conformance test here: http://test262.ecmascript.org/
Tests To Run: 10935 | Total Tests Ran: 10935 | Pass: 7061 | Fail: 3874 | Failed To Load: 66
The fast majority (80%) of the error log appears to be in section 15.2.3, with half of the rest also being in section 15. This would imply that around 1/3 of the entire test suite is just in that section of the specification; as the test itself describes, its coverage is currently incomplete.
Overall, I have to say, I am a huge fan of having these thorough tests come to web standards. So that browsers can't just say "We support HTML5". I am really tired of the buzzword nature of standards recently. Hopefully, this will get all browsers to step up their game.