Update: I ran Spybot 1.6.2 and Malwarebytes and removed all PUPs. Firefox still does not open or give an error message.

Before recommending a clean reinstall, does Firefox open if you run the Profile manager from the cmd.exe as an admin?

• Profile Manager - Create, remove or switch Firefox profiles

Attempting to run "C:\Program Files (x86)\Mozilla Firefox\firefox.exe" -p returns the same result... nothing. As I mentioned above, I have uninstalled and reinstalled the program once already.

Is there an antivirus or setting in the operating system that might be blocking the program from starting?

• https://support.mozilla.org/en-US/kb/firefox-wont-start-find-solutions#w_...

I have no idea. It's been working for years. Then I updated and it wouldn't open. Nothing is changed in my antivirus, and I can't run the profile manager. I need to find the settings that are left after an uninstall and delete them I guess.

One last try: Diagnose Firefox issues using Troubleshoot Mode

In order to preserve the profile, make a copy of the profile folder before a clean reinstall: Back up and restore information in Firefox profiles

Note: You might want to print these steps or view them in another browser.

1. Download the latest Desktop version of Firefox from mozilla.org (or choose the download for your operating system and language from this page) and save the setup file to your computer.
2. After the download finishes, close all Firefox windows (or open the Firefox menu and click the close button ).
3. Delete the Firefox installation folder, which is located in one of these locations, by default:
   • Windows:
     • C:\Program Files\Mozilla Firefox
     • C:\Program Files (x86)\Mozilla Firefox
   • Mac: Delete Firefox from the Applications folder.
   • Linux: If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install Firefox on Linux. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder firefox in your home directory.
4. Now, go ahead and reinstall Firefox:
   1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

More information about reinstalling Firefox can be found here.

WARNING: Do not use a third party uninstaller as part of this process. Doing so could permanently delete your Firefox profile data, including but not limited to, extensions, cache, cookies, bookmarks, personal settings and saved passwords. These cannot be easily recovered unless they have been backed up to an external device! See Back up and restore information in Firefox profiles.

Please report back to say if this helped you!

Thank you.

I moved my profile folder and renamed the Mozilla and Mozilla Maintenance folders, then installed Firefox. No change. I then tried to download the Adobe Flash Player update .exe file. The system will not let me Save or Run this file. Clearly these things are related. Obviously some nasty root kit has been installed and it has avoided detection by Spybot and Malwarebytes. It has also prevented me from enabling AVG.

Indeed there are also other malware programs that might be helpful, otherwise I would recommend talking to a technician.

You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• I took off Malwarebytes since it was not detected.
• Anti-Rootkit Utility - TDSSKiller
• AdwCleaner (for more info, see this alternate AdwCleaner download page)
• Hitman Pro
• ESET Online Scanner

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one. Windows 8 has antivirus built-in already.

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Did this fix your problems? Please report back to us!

TDSSKiller turned up nothing. Hitman Pro just removed the ASK toolbar and related files. None of these programs can find any virus or malware, yet Firefox doesn't run and I cannot install any Flash Player update. My system won't even let me copy the Flash update .exe to the local hard drive. I got the Access Denied message in the attachment. I was only successful after renaming it, copying it, then renaming again. Then I got the Cannot Access message in the attachment. This is my wife's system and she, of course, has no idea what she might have clicked to create this problem. At this point I'm thinking it's time to upgrade to Windows 8 (I'm running 7 64 Pro).

UPDATE: I was running AVG 2012. Specifically, it was installed, but whatever virus this is would not allow me to turn it on. I just now installed AVG 2015 and, after a reboot, I got a message the the Flash installer was now unblocked and no longer considered a threat. I then installed it without incident. I am running another full system scan now, this time with AVG 2015. I'll let you know if anything changes.

If it were me, I would:

Get the current, stand alone version of FF . . . https://www.mozilla.org/en-US/firefox/all/?q=english

Get the current, stand alone version of Adobe Flash Player (the non-IE, plugin based browser version) . . . https://www.adobe.com/products/flashplayer/distribution3.html

Get CCleaner . . . http://www.piriform.com/ccleaner

1.) Do a Restart 2.) Disable anti-virus and malware programs 3.) Uninstall Firefox and Adobe Flash 4.) Install CCleaner

5.) Run CCleaner on the Registry 6.) Do a Restart

7.) You could try Installing the previous version of FF you had, and see that it works, or just try installing the current version of FF . . . then install Flash . . . do a Restart . . . make sure anti-virus is re-enabled

Last update: After getting Flash Player to install, I decided to try uninstall/reinstall with Firefox again and I uninstalled AVG 2012. And now, magically, it works. AVG 2015 found nothing in its full system scan. I have NO idea what changed. My best guess is that there was something in AVG 2012 that was blocking FF v. 36. Wish I could provide more insight. Thanks to everyone for all of your suggestions!!!