A possible cause is security software (firewall,anti-virus) that 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 internet for Firefox and the plugin-container process and the updater process.

See:

• https://support.mozilla.org/kb/Server+not+found
• https://support.mozilla.org/kb/Firewalls

Try a clean reinstall and delete the Firefox program folder before reinstalling a fresh copy of Firefox.

Download a fresh Firefox copy and save the file to the desktop.

• Firefox 20.0.x: http://www.mozilla.org/en-US/firefox/all.html

Uninstall your current Firefox version, if possible, to cleanup the Windows registry and settings in security software.

• Do NOT remove personal data when you uninstall your current Firefox version, because all profile folders will be removed and you will also lose your personal data like bookmarks and passwords from profiles of other Firefox versions.

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

• It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.
• http://kb.mozillazine.org/Uninstalling_Firefox

Your bookmarks and other profile data are stored in the Firefox Profile Folder and won't be affected by an uninstall and (re)install, but make sure that "remove personal data" is NOT selected when you uninstall Firefox.

If you keep having problems then also create a new profile.

• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Profile_backup

• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall

We have the same problem in our environment with 900 users.

The problem is caused by our profile redirection. Our users connect on Windows XP and Windows 7 workstations to an Active Directory. To have their roaming user profiles working on XP and 7 we use a folder redirection for their profiles to a separate place on our storage.

%APPDATA% is therefor <ip-adress>\redirect-folder$

Here is the Firefox profile located under <username>\Appdata\Mozilla\Firefox\Profiles

Under this location now somehow the search engine entries for Firefox 20 mess up. That is why "Enter" does not work for restricted users.

When we delete the Firefox profile with firefox.exe -p and add a new one with a folder location somewhere on the c:\ drive everything works fine again.

Could you guys at Firefox fix this, please?

Many thanx

marxx