>> Browsers are not the right tool for sandboxing applications.
Browsers have been picking up the slack where OS and desktop developers have fallen down. The OS is supposed to handle process isolation and resource access, but here we are. Tabbed browsing became a thing because GUI toolkits didn't do multiple app instances (or MDI) in a way people liked.
When the browser first came out, the OS didn't even have a native TCP/IP stack! The internet was an app you installed. For a long time the core purpose of the browser was to pickup the slack/gap in the OS treating the internet as a first class thing.
Now, as the internet clams down a bit, the OS handles everything natively, including the security primitives (at least on mobile) and so the purpose of the browser is sadly diminishing. It's a less useful experimental side channel to the OS.
Browsers have been picking up the slack where OS and desktop developers have fallen down. The OS is supposed to handle process isolation and resource access, but here we are. Tabbed browsing became a thing because GUI toolkits didn't do multiple app instances (or MDI) in a way people liked.