Hi Zeppale, thank you for your bug report and I'm sorry the game doesn't load! As volanskie also has the same problem, this seems to be a common problem on Safari. I'll try to lend a Mac and see if I can fix it, but for now: maybe you could try to play on another browser if you have one?
Also, if you could look in the developer console of your browser for any errors and PM them to me, that would be great!
Hold UPGRADE button for half a sec.