And it's clear that they were looking at it from the start. If you read around a bit, you'll see that they ran into a particular performance problem with Firefox. They're working to solve it, but decided they could release something usable for Chrome users immediately.
They didn't even take the first step to solving it, which is filing a bug about it with Mozilla. When they mentioned the problem on HN, a Mozilla developer filed the bug for them and fixed it within a few hours.
So had they been _working_ to solve it, it would have been solved long ago. Like within days of them encountering it (adding some extra time to pin down the problem, which they _did_ do before not bothering to tell anyone about it).
Still, I suspect Google’s developers are too focused on development in Chrome-only. If true, this may have contributed to perf issues arising in Firefox, in the first place. I also suspect that Google’s web compat team is not sufficient to handle their products.
Did you read the clearly documented technical details? Basically, array slicing on sparse arrays in Firefox is much, much slower than on Chrome.
It's not a matter of lacking competence or skills or anything of the sort. It's a basic question of what level of resources you are willing to put into a product before you have something to beta-test. Inevitably, that's less than the amount required to be perfect in every aspect.
