I like your comparison about Firefox not being a great example of "good" C/C++.
I'd personally consider myself comfortable in C/C++. I've built Wayland compositors, H264 backends for live-streaming, and built Chromium occasionally for testing. Despite being a die-hard Firefox (zen) user - I still have not been able to compile Firefox! To be fair, this was pre-Firefox quantum days so I hope their SVM and build tools have improved.
I'd personally consider myself comfortable in C/C++. I've built Wayland compositors, H264 backends for live-streaming, and built Chromium occasionally for testing. Despite being a die-hard Firefox (zen) user - I still have not been able to compile Firefox! To be fair, this was pre-Firefox quantum days so I hope their SVM and build tools have improved.