Try updating your operating system.
Otherwise try to play it with Chrome: the WebGL version is a little bit slower and could have some minor problems but it's fully functional.
I rephrase my previous comment... Unplayable on a dual-core computer. I get a massive freeze for good 2 seconds at a time every time I swing the sword. 1/5
Has similar problem as on one of the latest Final Fantasy games: I've spent almost 100k gold to upgrade my gear, so I feel super hesitant to change for a better weapon. Also needs a key to return from the map to game (eg. press "4" again or "esc")
Try updating your operating system. Otherwise try to play it with Chrome: the WebGL version is a little bit slower and could have some minor problems but it's fully functional.