Earlier quoted context omitted.
Come on, that's not much more than a year old. > Firefox ESR > October 23, 2018
Firefox 60 is from May 2018. It's 12 major versions behind. You may not like it, but it's a fact that web browsers change quickly these days. Mozilla may support ESR for a year but I don't. This is a side project and my test matrix is already too large; I don't have time to test uncommon versions of each browser.
I'm just a little surprised that Firefox would have changed enough since last May to break your site.
And there's also the other tweaks I've made. For example, I don't allow WebGL or WebRTC. And I spoof referrer to a site's root. Plus other stuff that I don't recall offhand.
But anyway, now I'm curious, so I'll test in some otherf VMs, with different browsers.