This is debatable.
Web components is implemented in Chrome because it was a spec pushed by Google, so they had an implementation being built while things were still being decided. Firefox has an implementation too, just not turned on by default (presumably folks are waiting for the standard to settle?). Similarly, Firefox used ES6 internally for years, so any lag that may have existed (I don't recall any, but ICBW) would probably again be due to standardization. Chrome might be ahead in the implementation of features. You can't call them Web Platform features if they've not been standardized fully.
> and a large number of CSS properties.
Chrome being ahead in a "large number of CSS properties" is objectively false. I keep track.
Firefox has 324[1] properties implemented (I am not counting prefixes as separate properties) when I last counted (a few months ago), Chrome has 304[2]. Firefox has 88[3] properties not in Chrome and Chrome has 68[4] properties not in Firefox. Furthermore, if you look closely most of the Firefox-but-not-Chrome properties are solid green in the Firefox column, which means that they have been implemented in an unprefixed form (which in turn means that the property is probably specced and stable), whereas nearly half of the Chrome-but-not-Firefox properties are light green, which means that they're only implemented in the prefixed form, so the property is either custom or unstable.
I'll admit that these numbers are generated from Firefox Dev vs regular Chrome and Firefox dev has newer features enabled. I made that page to get an idea of Stylo/Servo progress and to help inform what stuff folks should work on next, not for comparing Chrome and Firefox.
Running in Firefox stable to get fairer numbers gets me 301 properties enabled, 69 Firefox-but-not-chrome, and 72 Chrome-but-not-Firefox. This does mean that Chrome has a slight higher number of properties implemented when comparing stable versions. 3 properties is certainly not "a large number of CSS properties", and again, many of the Chrome-only properties are prefixed and will either never be implemented or are unstable and have good reasons for not existing in Firefox.
The numbers aren't perfect. In particular handling implemented-but-disabled properties, properties that are still getting standardized, and properties that will never be standardized is tricky and can't be done in an automated way. But the numbers should be close enough, enough to say that at the very least Chrome and Firefox are at par when it comes to implementing CSS properties.
[1]: https://manishearth.github.io/css-properties-list/?stylo=sho...
[2]: https://manishearth.github.io/css-properties-list/?stylo=sho...
[3]: https://manishearth.github.io/css-properties-list/?stylo=sho...
[4]: https://manishearth.github.io/css-properties-list/?stylo=sho...