Thank you very much for the kind words! It was my first time making something even resembling a platformer, so it was really surprising for me how hard it was to get the jump to feel "right", and I wasn't completely certain it does in the end.
I didn't edit the HTML file (at least not for that), but I'm not exactly sure what you mean. The Unity web player seems to be the one handling the fullscreen, I'm honestly not 100% sure how. But the game in Unity adapts to any resolution, so seems like a natural extension of it.
Interestingly enough, on itch it is a bit blurry. I couldn't figure out why, it's absolutely crisp when just loading it on an empty page. But when you go into fullscreen mode, it's crisp again. Perhaps it's something to look into further.