Also, this is a Windows XP machine. I also ran in Safe Mode with Networking and had the same issue.

Try to open Firefox with the about:support page by creating a copy of the current Firefox desktop shortcut and add a space and -url "about:support" to the target field if that allow to post your troubleshooting information.

You did delete the Firefox program folder to do a clean reinstall?

Did you disable all plugins as well (never activate)?

• https://support.mozilla.org/kb/Troubleshooting+plugins

Does it help to open a new window (either normal or Private Window)?

Actually, let me try and set "about:config" and/or "about:support" as my home page.

Also, I went back through my Norton 360 logs and discovered that Norton 360 had quarantined xul.dll earlier this evening claiming that it had Suspicious.Cloud.9.B attached to it. Keep in mind that I have since uninstalled and reloaded Firefox twice, but Firefox ran fine before that time stamp.

I did disable all plugins and tried new windows to no avail.

Setting "About:Support" as the home page worked. Below is the text:

Application Basics

Name: Firefox Version: 36.0.1 User Agent: Mozilla/5.0 (Windows NT 4.10; rv:36.0) Gecko/20100101 Firefox/36.0 Multiprocess Windows: 0/1

Crash Reports for the Last 3 Days

All Crash Reports

Extensions

Graphics

Important Modified Preferences

Important Locked Preferences

JavaScript

Incremental GC:

Accessibility

Activated: Prevent Accessibility:

Library Versions

Experimental Features

There is no data present and that would suggest that all JavaScript is blocked.

Try to install Firefox in Windows Safe mode and make sure to delete the Firefox program folder.

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen).

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/

• Download the full Firefox installer and save the file to the desktop
  https://www.mozilla.org/en-US/firefox/all/
• Start the installation with a double-click on the desktop icon

I did delete the Firefox folder to do a clean install, twice.

Interestingly, if I create another windows profile and run Firefox, it works with no problem. If xul.dll is quarantined by Norton, does that mean it is always quarantined, even with a clean install? I don't believe that is the case because Firefox works on the other windows profile.

https://community.norton.com/en/forums/problem-firefox-3601-update

Did you try to install Firefox in Windows Safe mode?

If Norton is blocking some files that this shouldn't happen in Windows Safe mode. If it still happens in Windows Safe mode then it is more likely that you have a malware problem

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

If using various malware scanners does not fix it or if you are blocked from installing those scanners then ask advice at a forum that specializes in malware removal.

• http://forums.majorgeeks.com/index.php - MajorGeeks Support Forums
• http://www.security-forums.com/index.php - WindowSecurity.com Security Forums
• http://www.bleepingcomputer.com/forums - Bleeping Computer Forums

I deleted Firefox and installed in Safe Mode. Still no luck.

As mentioned in my original post, I scanned for malware using the multiple sites listed above. None found.

Also, as posted above, if I create another windows profile and run Firefox, it works with no problem. It is only if I run Firefox in my profile that the problem manifests itself.

Another thought, is there a registry key that disables the enter key when used in the address bar?

One more point of interest, I tried loading the No Script add-on back in. It downloads and asks for restart, but after restart never installs.

Create a new profile as a test to check if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/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 copied my profile files to another directory, deleted ALL profiles, uninstalled Firefox (4th time), searched for and deleted all Firefox or Mozilla directories and deleted them, restarted then when into the registry and deleted all I could find related to Mozilla or Firefox, then reinstalled Firefox and started fresh with a clean profile. Still doesn't work.

I have run all the malware programs listed and deleted all cookies multiple times now. This has gone beyond stupid.

I have Windows XP set up with two user profiles. When I run my wife's profile, Firefox functions as it should. When I run my profile, it doesn't.

Other bizarreness:

- Under "tools", "Options", "Search" I cannot "Restore Default Search Engines"

- Under Add-ins, I can download "Add-ins" but when I restart, they don't load.

Since this appears to be Windows profile dependent, I suspect that there is some registry value that is either corrupt or switched to disable address and search in Firefox. That is the only thing I can think of.

Hi indoorwthrman, since your Windows identifies itself as "Windows NT 4.10" (Windows 98) instead of Windows XP, could you check something. Right-click your Firefox program shortcut, choose Properties, then the Compatibility tab. If anything is selected here, deselect it, you don't want Firefox to run without the full capabilities of Windows XP. If you made changes, try exiting Firefox and starting it up again to see whether it makes any difference.

Jscher, YES! That was it!

In my search for a fix on this forum, someone had suggested running in Windows 98 compatibility mode. I never went back to unclick it and return to "normal" mode. This makes total sense now why it worked on my wife's profile but not mine.

Thank you!

Found where the problem actually is on my system. What I did: Clean Windows install. Clean firefox install. Enter was working. Restored profile from backup. Enter wasn't working anymore neither in normal mode nor in safe mode. Went to Addons. Clicked on "Check updates". (it updated "Html Validator" extension) Restarted Firefox. Enter key works again.