Replacements for mozrepl?

[Eric Abrahamsen]

I am finally admitting to myself that it's time to learn some javascript
(es6 isn't that bad). While poking around in js.el I found references to
a "mozrepl" package that would let me use Firefox as a repl. That
package appears to be this, which says it's end-of-life:

https://github.com/bard/mozrepl#readme

And recommends that we "investigate migration paths".

Has anyone done that? Is there a replacement/reboot of mozrepl? Is it
even possible in newer versions of Firefox?

Thanks,
Eric