>  I think the changes to that function in #37 won't work for env vars, is there a test for that?

I don't understand this question. Yes there are tests for `normalizeBinary` function, but I think
you misunderstand what the expected behavior is. Given `binaryPath` takes a priority if `undefined` then it will fallback to `env.JPM_FIREFOX_BINARY` if that's undefined too, then
fallback to `firefox`.

In this case though we want behavior to be `env.JPM_FIREFOX_BINARY || "nightly"` though that is why we define `binary` here to pass that in.