When you say processes, do you mean applications (only two running) or processes (long list) are you clicking on the processes tab and then clicking the cpu column twice to get the cpu hungry processes to the top?
If not, then try that and see what comes out on top.
Firefox did lose the plot on my pc about a year ago and started using as much power as it could lay it's hands on, I uninstalled firefox and reinstalled it using the latest version, sorted the problem right out.
Currently reading:- The tea leaves
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