It's not "as good." I've tried every release of Firefox for the past decade. On Linux and Mac the video performance is noticeably worse than Chrome with significant frame drops, lag, and tearing. Yes, I've tried enabling/disabling hardware acceleration, flash, and all sorts of other flags and options, but the two are still incomparable. Furthermore, even with the quantum update Firefox is still slower for general web browsing and usage than Chrome. I've measured both dropped frames and load times to confirm this.