(I'm using a desktop with Windows 10 without the recent disservice pack update.) This issue is a recent development, even newer than the weird sans serif font issue that began with Firefox 90. The issue is intermittent. When I scroll down a page using the wheel on my Logitech M510, parts of the page will refresh at different speeds. Usually this is noticeable as the illusion of a diagonal line and disappears as soon as scrolling stops. Sometimes part of the prescrolling display will remain rather than changing with the rest of the screen, usually as a rectangle. I've also started getting only partial display of dialog boxes when editing in Wikipedia, in which only part of the image changes. The rectangular area not updated is usually near the centre of the screen. The Wikipedia box issue has the opposite issue - the only part of the box that appears is in the same spot that fails to refresh when scrolling. If I tap on an arrow key, the unrefreshed portion of the screen gets back in sync with the rest. The issue seems unrelated to website, occurring on Wikipedia, Facebook, and Google. I disabled the Proton interface within a week of its appearance because it wasted so much vertical screen space, if that's any clue.