That's from October 2006. It includes things like let/const, generators, iterators, and destructuring assignment.
For reference, ES5 was published in December 2009.
So, it's kinda like applauding Microsoft for supporting text-overflow:ellipsis first. It's something they added with IE6. It became part of the standards much later with CSS3.
> No, the reason is that Mozilla just added lots of stuff way before it got into the ES specs.
That's only part of the reason, the linked page notes which features had been added by Mozilla (generally feature-gated). The count is 5 items of syntactic additions (out of 12), and 0 of standard library additions (out of ~40)
Well, historically Mozilla has been the main driving force behind JavaScript's development so that isn't too surprising. Who knows how Eich's departure will affect that, though.
We're waiting for Harmony for like 7 years with Eich?
I guess, given from the utterly dissapointing stats in the Mozilla page, and the even worse situation on Chrome, that we're in for another 7 year wait.
http://kangax.github.io/es5-compat-table/es6/
Not surprising, given Google's stance for other languages.