Firefox isn’t dependent on C++ because Rust is insufficient, it’s because porting (IIRC) fifteen MILLION lines of code just doesn’t happen overnight, and isn’t a direct focus.
That’s precisely the issue, until and unless enough libraries are created in Rust with little to no dependency on C/C++, it won’t be a significant language but will just be something similar to Haskell may be bit larger.
So I still feel Rust needs another decade or two to be able to claim as C/C++ replacement, not at present.
This is exactly the problem Swift faced to replace Objective-c, in Apple eco-system where everything controlled by Apple. Rust has much bigger hill to climb to be really useful systems programming language.
