Which browser supports HTML5 best?

This comparison can be made quite easily by accessing this URL in the browser you want to test. It gives a number the maximum of which can be 555.

http://html5test.com/index.html

This was the score for the latest Microsoft Edge 25.10586.0.0 and MicrosoftEdgeHTML 13.10586:

This one was for Mozilla Firefox 44.0

Well, Firefox does a little better.

There has been a lot of progress made by Microsoft in the past few years.

http://hodentekhelp.blogspot.com/2013/08/which-is-best-browser-to-text-html5.html