I think of browsers these days on par with OSes. I mean, they provide a runtime to execute binary code (wasm). They do process management and scheduling. They do a lot of things which up until 15 years ago, we thought bongs to the realm of Operating Systems.

And history has shown that when you need to do that kind of low level code, it's nigh on impossible to achieve acceptable results with a garbage collected language. Many people tried, none really succeeded.

Hence why Rust was made