Yeah seems you are right. Can't connect via websockets. Console output:
Firefox can’t establish a connection to the server at ws://expo.stimulusreflex.com/cable. action_cable.js:241:25
Firefox can’t establish a connection to the server at ws://expo.stimulusreflex.com/cable. action_cable.js:241:25
One surefire way to tell is to try the site in Incognito Mode. You could also try on your phone, although admittedly most of the demos are still slanted towards desktop interaction. That's 100% on us and not the tech itself.