Selemium is noticeably slow, and "Full-stack JavaScript" is vital for our primary SlimerJS use case: taking screenshots of webpages.

As a sidenote, there's a very interesting docker container that gets Selenium up and running heedlessly with Chrome and Firefox:

https://registry.hub.docker.com/u/vvoyer/docker-selenium-fir...

Whilst it's still slow, to suddenly have headless automated acceptance tests on real browsers is incredibly cool!