Unity2D WebGL build - graphics only looking sharp in fullscreen

Hello,

I made a previous post about this but I've retired it as the subject has changed. I'm having a problem with every sprite looking blurry after I build to WebGL - they look great in the editor and a Mac build. I've been twisting my head with this issue, but today I found that the sprites actually look sharp when I put the WebGL to fullscreen. So it has something to do with resolution scaling, I think.

Is there a guide to solve this somewhere? I can't find any. Or can someone help?

Thanks in advance.