Firefox won't start - find solutions (2024)

Table of Contents

• 1 Specific error messages
  • 1.1 Mozilla Crash Reporter
  • 1.2 Firefox is already running but is not responding
  • 1.3 Your Firefox profile cannot be loaded. It may be missing or inaccessible
  • 1.4 Failed to read the configuration file
  • 1.5 XULRunner - Error
  • 1.6 There was an error launching the application
  • 1.7 Error opening file for writing…
  • 1.8 Other error messages
• 2 No error message
  • 2.1 Firefox will not start due to malware
  • 2.2 Firefox will not start due to security software
  • 2.3 Firefox will not start after installing add-ons
  • 2.4 Firefox previously worked
  • 2.5 Firefox will not start because of missing libraries

Failed to read the configuration file

This error is caused by a problem with Firefox program files. The solution is to remove the Firefox program and then reinstall Firefox. (This will not remove your passwords, bookmarks or other user data and settings which are stored in a separate profiles folder.)

1. Uninstall Firefox.
2. Delete the Firefox installation directory, normally found in one of these locations by default:
   • C:\Program Files\Mozilla Firefox
   • C:\Program Files (x86)\Mozilla Firefox
3. Use another browser to download the Firefox installer from the Firefox download page and install it. See How to install Firefox on Windows for details.

There was an error launching the application

This error indicates that either Firefox is not installed or your shortcut to it is incorrect. Make sure that Firefox is installed at the location specified by the shortcut. If it isn't, install Firefox if necessary, then modify the shortcut to point to the correct location.

Error opening file for writing…

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. You can either reboot the computer or, if you have an administrator account, you can execute the program as an administrator.

1. Find the firefox.exe program file in the Firefox application folder on your system.
2. Right-click the icon.
3. Select Run As Administrator…. Select The following user:. From the Username drop-down, select Administrator or another user that has administrator privileges. Enter the password required to log in to this account. Click OK.
4. The Firefox application is started using the administrator Windows account. The user that was used to log in to Windows at startup is still the active one.

Firefox will not start due to security software

• Outdated versions of Comodo Firewall or Comodo Antivirus security software (or a leftover file after Comodo was uninstalled) can cause Firefox not to start with no error message. Update Comodo to the latest version, if you have it installed. If Comodo software is not installed, check if there's a file called IseGuard64.dll or IseGuard32.dll in your C:\Windows\system32\ folder or your system drive and, if so, manually delete the file.
• If you use certain versions of ZoneAlarm or other Internet security software that includes a "Virtual Browsing" feature, it can prevent Firefox from starting. Check virtualization settings and clear the virtual cache, if your Internet security software includes this feature, or visit the software provider's support site for more help.
• Firefox may fail to start for some Windows users after updating, if AVG or AVAST antivirus is installed. For details, see this Techdows article.

Firefox will not start because of missing libraries

If you installed Firefox outside of your package manager, make sure that your system has the libraries listed in the system requirements.

Based on information from Browser will not start up (mozillaZine KB)