Changing the Firefox setting did NOT work.
Only thing I can find online about it in regards to RPG Maker is this thread: https://forums.rpgmakerweb.com/index.php?threads/error-your-browser-does-not-all...
I've been playing RPG Maker games on browsers for a while now and I've NEVER seen this issue in my life. It looks like it might be an issue when you deploy the game on your side.
Also: Tried this on Chrome, and got:
Error
Failed to initialize graphics.