Since updating to Firefox 141.0 (Win11), I've had issues with performance and on-screen behaviour of dynamic web pages/sites. The problems do not manifest on Chrome, or on a reinstalled version of Fx 140.0.4 on the same computer running at the same time (and with copy of original profile's data files, extensions etc.), they do manifest on a new Firefox 141.0 profile with only one tab open. The problem happens on dynamic pages (e.g. gmail.com, boardgamearena.com/lobby) but doesn't seem to happen on static pages. Note that this doesn't depend on page elements moving around the visible window (e.g. panels opening and closing). The manifesting problems: * Screen pointer rapidly switching between standard arrow pointer, mouse with index finger (clickable link) and serifed-style insertion bar, even when positioned on a part of the page that is not a link or a text box. Video (MP4, <1MB) showing behaviour at https://imgur.com/a/absjTh4. * Browser intermittently fails to respond to browser actions (mouse clicks, keyboard entry) * Small increase in browser CPU usage Problem is worse if general CPU usage (from other applications) is already high - low CPU usage reduces but doesn't eliminate the problem. (Established by changing my BOINC settings and/or snoozing BOINC and observing; I have a gadget that monitors CPU and other resource usage.) The fact that I can see the problem occurring on Fx 141 but have Fx 140.0.4 working fine at the same time on the same page, suggests that this is a Fx 141 issue. Regular malware scanner and an alternate found no issues. Happy to do more diagnostic testing if it's helpful.