The provided links only compare API coverage, while other domains (performance, security...) are important. Even so, Firefox is clearly trailing Chrome, its main desktop competitor. It's not surprising since I've heard that the latter has much more man-power. And the gap will increase.

I've looked at CanIUse, ignoring the features which are implemented but disabled by default. Chromes lacks 5 features the Firefox has. The biggest two are MathML and VirtualReality, which were both available as experimental features in past Chrome versions but were removed for lack of interest in publishing or maintaining them.

On the other side, Firefox lacks 25-30 features that Chrome has. A few of them are minor, but most of them seem complex.