Screenshot of bug. The other icons on the top right look crystal clear by comparison.
When using en.m.wikipedia.org on desktop (tablet mode I guess) the blue "issues" icon, the icon is effectively being scaled up on a Retina screen which makes it a bit pixel-y.
It a plain 1x/2x conversion though. The file is 34px and it's rendered at 24px. So it's not quite as bad as a 17px icon rendered at 2x, but it's also worse because it doesn't scale up very well at only half pixels.