Sorry if I created confusion. I meant that the game seems to not proceed further than the screen with "game" in the corner.
In-between leaving this comment and now I have change OS (now Linux Mint) and I am still using Firefox. I may retry playing to see if that's done anything.
Edit: seems to still be the case. I get a beep noise when clicking the "game" in the corner and nothing happens if I just wait. Played on an Asus laptop with an AMD Athlon GPU.