Can you open builtin pages like about:home and about:about?

It is possible that your firewall or other security software blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program. Remove all rules for Firefox and the plugin-container from the permissions list in the firewall and let your firewall ask again for permission to get full, unrestricted, access to install for Firefox and the plugin-container process and the updater process.

See:

• https://support.mozilla.org/en-US/kb/server-not-found-connection-problem
• https://support.mozilla.org/en-US/kb/fix-problems-connecting-websites-after-updating

Would the firewall be part of my McAfee security application, or the Windows security? I have both of them. I'm not sure where to look to check if they are blocking Firefox.

You should only have one firewall running at the same time. Maybe check this in the Security Center in Windows Control Panel.

yep, according to my Windows firewall, Firefox is checked and allowed. So I deselected it, closed security, then opened it up and selected Firefox again and re-tested. Still not working. The URL window basically doesn't allow any URL to input - it goes back to blank. As mentioned, I already uninstalled then reinstalled Firefox earlier today as well. This is very strange. I've been using Mozilla Firefox for years now, never had this happen.

You can create a new profile to test if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

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

Still no luck. I ran Defender and McAfee and a few others - not finding any malware. I wonder if I should just uninstall and try reinstalling another version? Firewall is on but allows Firefox. Perplexing.

It almost seems as if something is preventing any text at all from inputting into the URL box. I can't type anything in there and when I try to paste in an address, that also doesn't appear. That makes me believe there is some malware or something impeding Firefox but not sure how to ferret it out. Fortunately, it's not doing the same thing in IE.

This will probably be the best solution since seem to not be getting to a result. You need to go into the Control Panel and turn Windows Firewall OFF, Until that is done you still have a conflict.

Once it is turned off leave it off as Mcafee will handle the duties.

Then I suggest that you try this : https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings If that fails to work after testing please uninstall Firefox and download A Full Version Installer here : https://www.mozilla.org/en-US/firefox/all/

If that fails then you need to create a new Profile : https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

Please let us know if this solved your issue or if need further assistance.

You say scanned with a few others. You ware asked to use specific programs to scan, not to scan with Mcafee or with Defender.

Directions must be followed to be able to concluded this issue. If directions are not followed...... I think you get my point.

So please scan with what cor-el suggested as they are specific to Malware Issues. Use this URL instead of Softpedia https://www.malwarebytes.com /adwcleaner/

If it finds issues and you need help with that please go to the forum of the program that found the issues and post and then Wait. https://forums.malwarebytes.com/topic/9573-im-infected-what-do-i-do-now/ Do not post in more than 1 Anti-malware site.

Please let us know if this solved your issue or if need further assistance.

Try to open a new window to see if that window works.

Did you try to create a new profile to test if your current profile is causing the problem?

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

I followed all of PKshadow's suggestions, ensuring that Windows Firewall is off, uninstalling Firefox, then installing the 64-bit full version of Firefox, then creating a new profile and deleting the old one.

Now, I can actually type text in the URL field but still not hitting any sites at all. What should I try next? Should I now try one of the Malware scans as indicated previously?

Installing http://www.malwarebytes.org/mbam.php worked!!!! Thanks guys for your help.