Many browser rendering engines are built in C++, so C++ is parsing the HTML. My general point is that many web/internet techs that web devs interact with have C++ one abstraction level below for actual implementation.
In any case, Rust is basically C++ 2.0 to me because it is very much in the spirit of C++.
It is kind of ironic that Rust will outlive Firefox as Mozzilla's legacy.