If you face Mozilla Firefox not opening, first of all, you should see what messages are being displayed. Different problems display different error messages. If other Web browsers are working during this error, then check your connection settings, may be Firefox is unable to access the Internet. Other reason could be that, you have recently installed add-ons or troubleshoot your themes and extensions. In worse condition, you may need to create a new Firefox profile because the corrupt profile will always prevent Firefox from opening.
What are the Specific Error Messages for Firefox not opening?
User may receive a message stating “Error opening file for writing…” you can try logging in as an administrator. Go to the “firefox.exe” program file in Windows, right-click on it and select “Run as Administrator.”
Many times, the user has recently updated software, in that case they receive a “XU Runner – Error…” message. In this case you can use another browser to download and install the latest version of Firefox after deleting the old Firefox installation directory.
Change Proxy Settings
If Firefox is not opening, but other browsers are functioning properly, then check your proxy settings using below steps:
• Click the “Firefox” menu option at the top of the Firefox window and select “Options.”
• Go to the “Advanced” tab and click on “Network” option.
• Click the “Settings…” button in the Connection portion of the window.
• Click on “No Proxy” if you do not use a proxy.
• If you are using a proxy, reference web browser’s settings of another browser or Microsoft’s guide to proxy settings.
• Close the Connection Settings window.
• Click “OK” to exit.
Check Other Connection Settings
• Many Internet security software such as firewalls or antivirus programs blocks Firefox from accessing the Web. Mozilla Support has reported that recently updated Internet security programs also cause connection issues.
• Check your firewalls or software and see Firefox is not on the list of blocked applications.
• Connection problems on some operating systems can also be caused by protocol for accessing the internet such as IPv6. Disable IPv6 in Firefox. Type “about:config” in the address bar. Press Enter. Click the “I’ll be careful, I promise!” button on the warning page. Enter the about:config window. Type “network.dns.disableIPv6” into the Search box. Double-click the “network.dns.disableIPv6” button and set the value to “true” to disable IPv6
Themes and Extensions
Themes are applied to change the look of Mozilla Firefox and extensions add new features or enhance existing Firefox functions. When themes or extensions get corrupted, they cause Firefox not opening issue.
Open Firefox in Safe Mode. It will disable themes, extensions and hardware acceleration.
Firefox Profile Settings
Personal information of user is saved in preferences in a Profile Manager. When these settings get corrupted, delete your profile and create a fresh one. Use the steps below:
• Close Firefox.
• Press the “Windows + R” keys on your keyboard.
• Type “firefox.exe -p” in the Run dialogue box.
• Press Enter.
• Select the faulty profile. Click “Delete Profile…”
• Click on “Delete Files” option.
• Click on “Create Profile…” button in the Profile Manager.
• Following the onscreen instructions.