To open the game in full screen, press the key combination Ctrl + Alt and then F11. Or Fn + F11.
In order to correctly open the game in full screen, first you need to check “Always Show Toolbar in Full Screen” in the “View” tab.
Then press the key combination Control + Command + F.
In addition, if nothing from the above-mentioned helps you to open a game in Full Screen, please open it in the browser settings (e.g. below - Chrome)