Firefox and Chrome are both actually written substantially in JavaScript. It's possible that they could get away with JavaScript + C rather than JavaScript + C

Firefox and Chrome are both actually written substantially in JavaScript. It's possible that they could get away with JavaScript + C rather than JavaScript + C++ (conjecture here). In this world more stuff is implemented JavaScript perhaps. There is the saying that any sufficiently large program contains a buggy and ill-specified version of Common Lisp... I would rephrase that as any sufficiently large program needing to contain its own extension language and programming language. JavaScript is filling that role for the browser, and I expect there to be a language in the future that does it better. There won't be anything that replaces C (or C++). Go can't do it. But there will be something that works better with C and C++ for big performance-intensive applications. Lua is close. The reason I would prefer C is that C++ has a very hostile interface for another programming language to interface with. I wish Python were there, but it's C API isn't really up to the task, especially with regard to concurrency (which e.g. Firefox and Chrome have a lot of!).