Flickering windows Google Chrome and Firefox but not Safari
Tonight, both Google Chrome and Firefox windows flicker particularly up on the menu bar. I updated Firefox 71.0 and Google Chrome is at 79.0.3945.79. Safari does not flicker.
Earlier today, my cursor started jumping all over the window so I managed to do a SAFE boot which stopped the cursor jumping but I have to believe the two phenomena are related.
Yesterday, I could watch Netflix on Chrome with smoothly moving picture and synchronized sound. Tonight, the same video runs slowly, jumps from picture to picture and there is no sound. The same is true on Firefox. Because my computer and system are so old, Netflix movies will not run on Safari but Chrome has been working fine.
iMac 27", macOS 10.13