When you boot to Safe Mode with Networking, Firefox does come up and works.

That would seem to indicate some third party software is interfering with Firefox. Prime suspects are usually security related software. If that is not the case work through the list of things that startup in normal mode but not in Windows Safe mode.

What security related software is in use ?

Given that you also have high CPU usage and Firefox running you may need to consider the possibility of malware.

• is my firefox problem a result of malware
  • and advice on how to check this /questions/914980#answer-302372
• also see
  • firefox hangs (but that is not usually with high CPU usage)
  • firefox consumes a lot of cpu resources
  • firefox will not start

The system is running Norton Internet Security 2012. The system has been scanned by Norton, MalwareBytes Anti-Malware, and Spybot and tested clean. So I don't think malware is the issue, but I will scan it again.

1. Check and reset NIS 2012 settings, ensure it does not block Firefox.
   If that fails
2. Then Physically go off-line pull the plug or WiFi connection. Now that it is safe as you are not connected to the Web try with NIS2012 installed.

I uninstalled NIS2012 and firefox still gets caught in the CPU loop and will not open a window.

You know Firefox works when Windows Safe-Mode is used, but not when you start up Windows normally.

Unless someone else comes up with a suggestion I think it is down to a hard slog process of elimination. Look at all the things listed as starting when windows opens, and look in task manager at all processes that are running when you try each method. One of the additional processes is likely to be the cause of the problem.