This has happened over the last couple of days. If I don't boot Firefox, everything seems okay. But when I boot Firefox these random things happen.
Either the computer just shuts down, or it goes to hibernate.
All power saving settings are set so this will not happen.
If it shuts down, it just does that. If it hibernates, if I restart it fairly immediately, the computer then works normally for a couple of hours, then shuts down. If I don't restart it from hibernation fairly quickly, it just shuts down.