If using Firefox on Youtube then it is Firefox. It use to reboot my pc after it crashed when I left Firefox open during the day. I suspect on of the many add on’s I had was really doing it. I removed them and added back what I wanted (leaving several off) and the problem went away.
That's just it. It hasn't happened since I removed the YouTube Flash add on from Firefox and theoretically might not ever happen again. But there's no way to know that, and what happened should never have happened with a brand new computer anyway. I've been advised by several people, including one at the store where I bought it, to bring it back. For the same price I can have another computer with an Intel processor.
Everything I do here is a chance. If I don't return this tomorrow I never will, because it's the last day.
I really prefer to play YT with Flash in Firefox, btw.