Can't help with your window size question, but I can give you a couple notes on the controls having tried it for just a minute. Supporting both WASD and arrow keys is definitely nice. And having a keyboard option for firing is a treat. A surprising number of platformer "game devs" (on this site especially it seems) seem to forget that platformers games don't all need mice, and just use WASD + mouse when the mouse doesn't even make sense. So kudos on providing a control scheme that's more friendly to people on laptops or who just don't want to use a mouse!
That being said, you've got a bug in the controls, so the up arrow key doesn't jump, meaning I would have to try with the WASD keys... and W for jumping with Ctrl for firing doesn't make for a good combination in a web browser 🤣