Firefox used to have a "scratchpad" for doing code in the browser, albeit somewhat barebones. Unfortunately it was more or less abandoned and eventually removed

Firefox used to have a "scratchpad" for doing code in the browser, albeit somewhat barebones. Unfortunately it was more or less abandoned and eventually removed. It would have been nice to see it expanded instead. A full on node environment would be a bridge too far IMHO but it would have been great to have added a good way to reuse modules and some more GUI niceties. It did have full access to the current web page so there would have been security issues with new coders copy/pasting code from the internet. But a revised version could give it its own isolated environment by default.