It looks like the page only does a User-Agent check[1]. The sites under "The demo detects the following websites:" is just a list of sites that the demo has hardcoded support for detecting[2].
It is reporting "not affected" for me on Firefox stable and nightly. It does show a list of domains at the bottom that it would check if the brower was exploitable.
I assume safari is the only effected browser but the site itself gates on a user agent check, because of course it does.