[alwillis]

> Or is Firefox trailing even mobile Safari here?

Short answer: yes.

Here are some web platform features Chrome and Safari (desktop and mobile) are shipping but not Firefox:

* Container Style queries: https://web-platform-dx.github.io/web-features-explorer/feat...

* @scope: https://web-platform-dx.github.io/web-features-explorer/feat...

* Picture in Picture: https://web-platform-dx.github.io/web-features-explorer/feat...

* View Transitions: https://web-platform-dx.github.io/web-features-explorer/feat...

* Cross-document view transitions: https://web-platform-dx.github.io/web-features-explorer/feat...

[nonillion]

I'm not a developer, so maybe I misunderstand what PiP is strictly speaking. But, I thought I had been using PiP for a couple of years now in Firefox. https://support.mozilla.org/en-US/kb/about-picture-picture-f...

Is this not PiP?

[alwillis]

According to caniuse, it's a proprietary implementation that's only partially implemented [1].

[1]: https://caniuse.com/picture-in-picture