Apparently when Firefox updated to version 78.15.0 on my Devuan Chimaera operating system, I began to experience video corruption. Whenever the cursor is moved, thin horizontal lines break up the text or image for one second. Another symptom is that when the cursor is moved onto or away from the scroll bar at right, it displays horizontal lies of shades of grey. Other video intensive applications (LibreOffice Word) and browsers (tor browser, Chrome) don't have the problem. Hardware is Gibabyte Z590 Aorus Elite (no video card). I reinstalled without customization, cache, addons and the problem persists.