Good one. Didn't work for me since JS wasn't enabled for the site (FF-188.8.131.52+Noscript+Privoxy) but the site clearly states disabling JS doesn't mean it's not vulnerable. Reading https://bugzilla.mozilla.org/show_bug.cgi?id=360493
gives more examples (also it seems this got reported aprox ten days ago). FF devs appear (IMHO) to be more concerned with fscking up their UI / release schedule than fixing this in the next release.