Kind of deceptive because it shows months of improvements in Firefox against a current snapshot of other browsers. If you looked at the trajectory of other browsers, you'd see that they too are getting faster and more performant in JS, which means that Firefox is not catching up as fast as the impression this article gives.
If you check http://www.arewefastyet.com you'll see graphs of Firefox's trajectory vs. other browsers. It may look like the other browsers are standing still, but that's just because Firefox is legitimately improving at a much, much faster rate.
This is nice but I wish they would have done it two years ago when V8 first came out, it is sad that it has taken so long. I also hope they can continue to get the same performance improvements and become faster before release instead of just skimming right above everyone else.