This reminds me of the story of the "Feather" project at YouTube where they improved a lot the page weight and the average page latency went higher just because they were actually seeing a lot more traffic from places with slow Internet.
The ISP named Free in France also did this a while ago.
It was fairly well implemented I think: separated from your network, bandwidth was limited (to avoid impacting the host), you could opt-out (which meant opting out of using the guest network), joining the wifi was automatic if you had a cellphone with the same ISP and it was the same "guest" network for all routers so in big cities, you could rely only on this to access Internet.
It was stopped a few years ago when they deemed cellular network was reliable enough to not need the guest network.
A bit late to the party but there is a famous French internet show called "Faux-raccord" which does exactly what this article does: every episode is focused on mistakes for some movie, told by the duo Michel and Michel with some jokes along the way.
Biometric or password is necessary for every access (which may be an inconvenience for some).
Basically, the addon communicates with a native application on the OS (the iCloud application on Windows or the password application on macOS) so there is nothing stored in Firefox.
Like this: https://nitter.net/MaximeRivest/status/2073544461473169432
Both are running the same software but I guess the protection of the sites work differently.