> using UA sniffing to roll out Google+ features only to Chrome even when Firefox worked on them, conveniently breaking Google properties in non-Chrome browsers, etc.

You reminded me of when they broke Microsoft Edge[0] by adding an empty (useless) div over the video element. IIRC that ruined its hardware acceleration, too.

[0]: https://www.theverge.com/2018/12/19/18148736/google-youtube-...