Safari, Chrome, and Edge already partitioned the HTTP Cache by site; Firefox was the last major browser not to. It's great that Firefox is doing this, but it's not a differentiator.
> These impacts are similar to those reported by the Chrome team for similar cache protections they are planning to roll out.
"The feature is being rolled out through late 2020. To check whether your Chrome instance already supports it: ..."
Safari has been doing this since 2013 https://bugs.webkit.org/show_bug.cgi?id=110269
Tweeted about in 2017 https://twitter.com/cramforce/status/849621456111624192