At times, my whole PC becomes unresponsive, e.g., cannot switch to different programs or start task manager. Task manager shows the highest memory using program is firefox with steadily increasing usage. At this itime it is 564MB and updates with higher number every 2-3 seconds. I already restarted it and the PC. No new add-ins etc are added.

I tried to cleanup in about:memory but it does not show any effect