If you do not keep changes after a restart or otherwise have problems with preferences, see:

• http://kb.mozillazine.org/Preferences_not_saved

Do a malware check with several malware scanning programs on the Windows computer.
Please scan with all programs because each program detects different malware.
All these programs have free versions.

Make sure that 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: Home Page:
  http://www.microsoft.com/windows/products/winfamily/defender/default.mspx
• 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

I only ran Spybot, but earlier I had found the home page set in the mozilla.cfg file as follows:

pref("browser.startup.homepage","https://www1.posnet.com.ar/webpos-frontend/context/start");

I really don't know how it got there, but I commented it off, and now I am able to set the home page without any problems through the browser options.

Thank you for your prompt reply. I will continue to run the other malware programs.

There shouldn't be a mozilla.fcg file present unless you've created it yourself to initialize some prefs.

This also involves the presence of a .js (JScript) file, probably in "defaults\pref" folder, that specifies to process this mozilla.cfg file.

If you have .js files apart from the channel-prefs.js file, that sets app.update.channel, in the defaults\pref folder then open this file in an editor like Notepad and please post its content.

If you have this mozilla.cfg file then best is to do a clean reinstall and delete the Firefox program folder before reinstalling a fresh copy of Firefox.

• http://kb.mozillazine.org/Preferences_not_saved#Other_solutions
• http://kb.mozillazine.org/Locking_preferences

Besides the \\program files (x86)\Mozilla Firefox\defaults\pref\channel-prefs.js file, there is one called local-settings.js, its contents are:

pref("general.config.obscure_value", 0); pref("general.config.filename", "mozilla.cfg");

If I uninstall/install again, this would be the 4th time. This is a brand new laptop and when I got it from our IT dept. it already had this problem. The second time I uninstall and reinstall. The third time I uninstall and then deleted the files in the \\Users\(user)\AppData directory. I have been downloading it from www.mozilla.org. I will download one more time and delete the mozilla directory from the programs folder.

You can remove this local-settings.js file to disable using the mozilla.cfg file.
When this file is no longer present then you can remove the mozilla.cfg file as well.
If you would remove the mozilla.cfg file, but leave the local-settings.js then you wouldn't be able to start Firefox.
You can consider to leave the mozilla.cfg file, but set it to read-only.

I reinstalled one more time. The uninstall did not remove the local-settings.js, but did remove the mozilla.cfg file, so I removed the entire Mozzilla Firefox directory manually to get rid of the local-setting.js file, and now things are working normally. Thank you for your help.