The latest version of firefox, I guess.
edit: The game works in chrome.
I would suggest normalizing the player's speed when moving diagonally (so that he moves the same amount up or down as he does up-left or down-right etc)
Viewing post in A Game of Jam jam comments
Thank you for your feedback!
I agree, I should change the diagonal movement speed. I will do that! Thank you for pointing that out! I completely missed that!
As for the black screen, it seems like the game is incompatible with Firefox (and probably IE too). I know what the issue is, but I don't have enough time to fix it at the moment.