[arlort]

Something that would be cool to do, though I'm not familiar enough with build systems and profilers to do it myself would be mark which portions of the generated binary comes from Rust/C++/C and then instrumenting the executable to measure how much time is spent in each of those areas for a typical use of the browser

[klysm]

I bet you could do this with user space probes but it would be somewhat difficult so probably not worth the time.