This sounds like a system problem. https://support.microsoft.com

http://answers.microsoft.com/en-US/windows/forum/windows_10

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

I did this but the problem was still there. So then I tried the refresh, but it is still there. I have no add-ons.

Do you see this problem only when Firefox is the active window, or only when Firefox is running (even if it is not active window)?

It happens all the time, even when I first turn on the computer, even when the log in screen is on.

Sounds like malware. Our support article lists free cleaning tools you can use to supplement your regular security software. It also lists specialized forums where you can get more hands-on assistance.

Troubleshoot Firefox issues caused by malware

Do a malware check with several malware scanning programs on the Windows computer.

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware

Please scan with all programs because each program detects different malware. All these programs have free versions.

Make sure you update each program to get the latest version of their databases before doing a scan.

• Malwarebytes' Anti-Malware:
  http://www.malwarebytes.org/mbam.php
• AdwCleaner:
  http://www.bleepingcomputer.com/download/adwcleaner/
  http://www.softpedia.com/get/Antivirus/Removal-Tools/AdwCleaner.shtml
• SuperAntispyware:
  http://www.superantispyware.com/
• Microsoft Safety Scanner:
  http://www.microsoft.com/security/scanner/en-us/default.aspx
• Windows Defender:
  http://windows.microsoft.com/en-us/windows/using-defender
• Spybot Search & Destroy:
  http://www.safer-networking.org/en/index.html
• Kasperky Free Security Scan:
  http://www.kaspersky.com/security-scan

You can also do a check for a rootkit infection with TDSSKiller.

• Anti-rootkit utility TDSSKiller:
  http://support.kaspersky.com/5350?el=88446

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

cor-el: Thanks for all this links. Unfortunately, I still have the issue. After doing all the scans, I shut it down, and powered off the modem to update (hopefully). Screen went dark after 11 seconds. One more thing - can you tell me where to go to uninstall the .exe files? I found 2 of them in the Control Panel/Programs, but not the others. Then I tried c:program files/, but they weren't there either. Thanks much. You've all been very kind with your suggestions.

With Windows systems, there are two Program Folders.

C:\Program Files C:\Program Files (x86)