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

User Account opens up asking me each time if OK but FF never opens I am lucky if it does WEBroot firewall Mozilla is allowed to connect Windows defender is turned off .

Check that you do not run Firefox as Administrator.

Right-click the Firefox desktop shortcut and choose "Properties".

Make sure that all items are deselected in the "Compatibility" tab of the Properties window.

• Privilege Level: "Run this program as Administrator" should not be selected
• "Run this program in compatibility mode for:" should not be selected

Also check the Properties of the firefox.exe program in the Firefox program folder (C:\Program Files\Mozilla Firefox\).

OK thanks for the help will try this , I have fears of shutting down PC at night

cuz so hard to get FF going again ...............te

I found the only one checked was " compatability with Win XP 98 , so deselected

that one . now to close FF and see if it will open ??

I shut down PC Win 7, cuz never could get FF to open again , never when re-booted clik icon maybe 40 times One time the USER ACCOUNT WINDOW came up " allow mozilla " , then finally a window came up that FF had shut down unexpectantly and I could open it in Safe Mode , which is what I am in now . FF just toooooooooooo much trouble , have to go back to IE or Chrome I have patience, but not sit here for 30 minutes trying to get FF up and going .........te

Do a clean (re)install and delete the Firefox program folder (C:\Program Files\Mozilla Firefox\).

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

• Firefox 13.0.x: http://www.mozilla.org/en-US/firefox/all.html

Uninstall your current Firefox version, if possible.

• 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 elsewhere in the Firefox Profile Folder and won't be affected by a reinstall, but make sure that you do not select to remove personal data if you uninstall Firefox.

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

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