This benchmark is only representative for websites built with lots of new ES6+ features. On general JS performance, Firefox isn't quite that far behind (but still behind to the best of my knowledge).
And that's all fine...in a lab. In the real world, all I have to do to experience Firefox's performance is click "Home" on my Twitter account. More often than not I'll get an alert that "A script has stopped responding [...] Continue / Stop Script," and it will still take 60+ secs to finish refreshing the page. Meanwhile, all Firefox tabs and window instances are frozen.
That's more of an indication that Chrome monoculture encourages crap developer practices. There's no reason a messaging site should be so bloated that it brings a modern browser to it's knees.
I've had Firefox block more js/elements than Chrome and sometimes I think other bits of the page are busy waiting for some event that will never happen.
That's weird. Firefox is my first-choice browser, and it only takes a couple seconds to load Twitter. You might want to see if you have any badly behaving plugins.
re "all Firefox tabs and window instances are frozen" — looks like you don't have multiprocess enabled. Check about:support for Multiprocess windows and Asynchronous Pan/Zoom.
