I personally would also check if the libraries Firefox uses are Rust, I mean the browsers this days are huge, you have image,audio,video,WebGl,pdf and a ton mor

I personally would also check if the libraries Firefox uses are Rust, I mean the browsers this days are huge, you have image,audio,video,WebGl,pdf and a ton more features so you need all the dependencies to also be memory safe especially the ones that handle untrusted input.