@Jasper :-
I concur with m'colleague. Pale Moon is definitely the problem here.
You have to understand, Pale Moon arose due to a bunch of developers who didn't like the way Firefox was heading. Initially, it used the Mozilla 'Gecko' rendering engine, but latterly, they've developed their own, custom rendering engine called Goanna.
In addition to this, they now incorporate a lot of stuff from the UXP (Unified XUL Platform) Project, along with a stated determination from the PaleMoon project lead, Moonchild, that they will never, EVER include WebComponents and/or WebAssembly. He doesn't want to go that route, regardless of how much pressure he may get from community members.
They also have no intention of ever including DRM decoders like WideVine.....so no NetFlix, Hulu, Amazon Video, Spotify, etc, etc.
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It initially got included with Puppy because it was a nice, lightweight browser that was largely compatible with everything on the web, and didn't suffer the horrendous memory leak issues that Firefox was displaying at the time. Since which time, their code-base has been steadily diverging from that of Mozilla, and much of FF's current stuff simply isn't supported.
Personally, I think they're shooting themselves in the foot, but.....that's just me.
In all honesty, Chromium, Chrome and the 'clones' (Brave, Opera, Iron, Vivaldi, SlimJet, Yandex, etc, etc) pretty much rule the web nowadays. And you just know that if you use one of these Chromium-based browsers, then everything will just "work".
Mike.