[JimDabell]

> I don’t remember the last time I ran into something in Safari and Chrome but not FF.

It’s not especially uncommon. For instance payment requests, web share, and remote playback are all implemented by Blink and WebKit but not Gecko.

https://developer.mozilla.org/en-US/docs/Web/API/Payment_Req...

https://developer.mozilla.org/en-US/docs/Web/API/Web_Share_A...

https://developer.mozilla.org/en-US/docs/Web/API/RemotePlayb...

I occasionally look into what CSS is being transcoded for the projects I work on, and it’s normally Firefox ESR that needs the most help. If you eliminate that from your browserlists configuration, your source and deployed CSS become a lot more closely aligned. For instance, it was only a year ago that Firefox ESR got CSS nesting.