I have tried everything I can think of and everything I have been told on how to fix this. I finally went back to Safari. Firefox 79.0 (64bit). I sat today and watched Firefox with ActivityMonitor running and would go from website to website seeing how often Firefox would freeze the entire mac up. I thought it was just the mouse that was being frozen, nope, it is the entire mac. Everything stops when this freeze occurs. Today I experienced the longest freezes. One lasted over 20 seconds. I will keep my eye on updates to see if this problem gets fixed. Until then, back to Safari :-(