This is a legitimate question if you really know the answer or can provide some information.
Firefox and Chrome are continually working to include many of the features in ES Harmony...
My question is really 2 parts:
The draft is supposed to be feature-complete roughly by the end of this year, and the plan is to finalise the new standard by end of next year. How long it will take browsers to fully implement it is another question (ES6 is gonna be pretty large).
I certainly cannot answer (2), and I suppose even MS themselves cannot at this point. But I know that they have started prototyping some features, like block scoping.