Everything starts looking weird

I have a problem.
All my costums are looking distorted.
Normal: Feuerball|16x16
After playing a while: Unbenannt
The problem is, that the background is now visible and distorted.

Please explain more than "my costumes are looking distorted".
For example, take a screenshot, and explain what you were doing before the costumes looked distorted.

I'm pretty sure this is a result of repeated anti-aliasing. Did you change the costume size a few times?

On my list of things-I-want-but-will-never-talk-Jens-into is a way to turn off anti-aliasing.

browsers cannot "turn off anti-aliasing".

Huh. Is that because the line-drawing code is in the operating system rather than in the application? I can turn off anti-aliasing in Photoshop; I do it often.

What's the "huh" about? I didn't decide that. Read the spec: https://html.spec.whatwg.org/multipage/canvas.html#2dcontext

The "huh" was "I was expecting an argument why we shouldn't do it, not an argument that we can't."

Isn't " Image smoothing" about anti-aliasing?