Also, the browser running the game is Firefox, not Chromium-based. So that is another possible source of an issue too. Sometimes I've run into problems with running Godot games under Firefox, but not frequently so.
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For sure, it could be a browser issue, or a game engine / game SDK that is optimized only for Chromium browsers. I heard once that because of the dominance of Chromium browsers on the internet, some developers (i.e. game engine authors) only test with the Chromium line of browsers and don't test with others very much if at all. It could just be the game engine itself. But in any case, that's good that it has been narrowed down / isolated as the probable cause.