My go to for most of what you mention is Go, but that’s obviously a compiled language and not for scripting. Or is it - What do you think about https://github.com/traefik/yaegi, which provides an interpreter and REPL for Go? It would let you use a performant and well documented language in a more portable scripting way, but not preclude you from generating statically linked binaries if and when that’s convenient.
I didn’t know they’d be able to tap into the Firefox profiling tools, that’s neat! Probably great data to have as they get into debugging of more complex websites.