[nwallin]

They are '90s codebases, they're not just "like" '90s codebases. Firefox obviously dates back to Netscape, and webkit (which Safari, Chromium, Opera, Vivaldi, and now Edge are based on) is a fork of KHTML.

Mozilla could have achieved 90% of what it wanted from a rust rewrite with a modern C++11 rewrite at a quarter of the cost. Linter rules that say "no new or delete", "either unique_ptr<T> or shared_ptr<const T>", and "only construct unique or shared ptr via make_unique and make_shared" get them like three quarters of the way there.

The thing that makes rust great is that the static analyzer is built into the compiler and has strict defaults. C++ is the same language, but clang-analyze and clang-tidy are shipped as separate packages and have more permissive defaults.

[pcwalton]

Those rules are completely insufficient. It's worth looking at the actual vulnerabilities here.

There is a reasonable argument that modern C++ is less safe than old C++, because features like lambdas are very prone to use-after-free.