Firefox prevents going into hibernate mode. It only appears to blank screen until mouse is moved or lid moved. This happened on 3 year old dell and now on new lenovo. I've gotten around it by going into task manager and killing firefox before hibernating. This doesn't happen on a newly opened window. I've noticed that as you use it, in the task manager, (not sure of correct term) the amounts of firefox tasks/threads? increases but does not decrease when tabs are closed. Eventually hibernate stops until I kill the firefox program. I thought this might go away with new lenovo with twice the ram, but happens at same rate. If I forget to kill firefox, I end up with a dead battery. This doesn't happen with edge or other browsers I've tried.