After using 20.04 on this machine for months with no problems, following a full package update today, the browser scroll position jumps around, usually to the top, without any mouse input and even with the mouse disconnected (Firefox and Chrome). It jumps once every few seconds, but sometimes acts normally for a few minutes, but then resumes the bad behavior. Reading or interacting with a web page is extremely difficult when this happens.
This behavior has been described before, but no explanations or solutions have been forthcoming.
Cursor jumping to top and bottom of page for multiple browsers in Ubuntu 20.04
All browsers are jumping around web page after updating to 20.04