I suggest that it is a software problem. Probably one of your add ons. It appeas that there is some infintite loop which is executing but I have no idea of exactly where the issue lies. One of the issues I have had for several years is that Abode Flash continues to crash, even witht he latest version installed.
My computer cools off when I close and then restart Firefox. Admittedly I do have 25 tabs open normally but I doubt that this alone is the proble.
To hlp cool you machine I put an empty glasses case underneath the back so that air can better circulate. If you maching gets ultr hot then you may wish to stand the machine on its end so that the hot air escapes beter again. I know this is drastic but it should help. Also, maybe close the lid and then open again. All works in my case although this should not need to be done..........but what else does one do when one has an issue which developers like Adobe refuse to fix.
Good luck.