[predakanga]

Yep, Mozilla Prism - there have been plenty of similar efforts both first- and third-party: https://en.wikipedia.org/wiki/Site-specific_browser

They may even retain some use - on OS X, for example, you used to get issues with PWAs being considered part of the main browser process for cmd+tab and cmd+`. I've had to use SSBs to overcome this in the past.