Well…
Yes, I have come to the conclusion that is more kind of an upstream problem: when you take a look on the web for font.name-list.emojiand/or layout.css.font-variant-emoji.enabled you can find quite some discussions (older and recent ones!). I am not the only one noticing and remarking. This seems to be a known issue. But I haven’t got the idea/background of it. I some notes it is also said that it seems related/could be related to Anti-Fingerprinting measures…