The user that was used to log in to Windows at startup is still the active one. The Firefox application is started using the administrator Windows account.Enter the password required to log in to this account. From the Username drop-down, select Administrator or another user that has administrator privileges. Find the firefox.exe program file in the Firefox application folder on your system.You can either reboot the computer or, if you have an administrator account, you can execute the program as an administrator. If you receive the above error when launching Firefox on a Windows system, you may be required by Firefox to log in as an administrator. If Firefox still does not start, see the Firefox will not start due to security software section below. If you see the message, 'XULRunner - Error: Platform version is not compatible with minVersion '' ('' depends on version number), after a software update, use another browser to download the Firefox installer from the Firefox download page, save it to the desktop or other location, delete the Firefox installation directory and then reinstall Firefox reinstall Firefox reinstall Firefox. See How to install Firefox on Windows for details. Use another browser to download the Firefox installer from the Firefox download page and install it.Delete the Firefox installation directory, normally found in one of these locations by default:.(This will not remove your passwords, bookmarks or other user data and settings which are stored in a separate profiles folder.) The solution is to remove the Firefox program and then reinstall Firefox.

This error is caused by a problem with Firefox program files. See How to run Firefox when your profile is missing or inaccessible for solutions. See 'Firefox is already running but is not responding' error - How to fix for solutions. If Firefox closes or quits unexpectedly as soon as you open it and the Mozilla Crash Reporter appears, see Firefox keeps crashing at startup for solutions.įirefox is already running but is not responding Specific error messages Mozilla Crash Reporter 2.5 Firefox will not start because of missing libraries.2.3 Firefox will not start after installing add-ons.2.2 Firefox will not start due to security software.2.1 Firefox will not start due to malware.1.6 There was an error launching the application.1.4 Failed to read the configuration file.1.3 Your Firefox profile cannot be loaded.1.2 Firefox is already running but is not responding.

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