My understanding is that WebKit (Safari) and Blink (Chrome) both have extremely complex smart pointer types and GCs and allocators such that they count as memor

My understanding is that WebKit (Safari) and Blink (Chrome) both have extremely complex smart pointer types and GCs and allocators such that they count as memory-safe, at least in comparison to regular C++. I don't know how much this applies to Firefox but I would assume they have similarly elaborate infrastructure. Large portions of each browser are also written in JS ("self-hosted") at this point, and Firefox now contains large components either written in Rust or sandboxed (via wasm) C. This rule does seem like an easy way to reject literally every browser other than Servo, though.