I had a lot of difficulty giving the WASD input. Switching to another tab or another application didn't help. Refreshing (F5) didn't help. Clicking on the game didn't help. Only a thorough refresh (CTRL+F5) helped. And I couldn't figure out how I could fullscreen the game and give WASD input at the same time. (Firefox 75.0 on Ubuntu 18.04).
Very cute looking game though!