Because standards conformance tests always have maximum and minimum possible scores, we can divide the result by the maximum score and multiply by 100 to get a percentage. This allows us to easily average the results of each conformance test to come up with a composite grade.
Chrome lands in first place with a solid A. Firefox takes second place followed by Opera, both achieving a B. Standards conformance falls dramatically from there, with IE9 and Safari both earning Fs to finish in distant fourth and fifth places.
The charts below are for the three standards conformance tests: Ecmascript test262, HTML5Test.com, and Peacekeeper v2.0 HTML5 Capabilities.