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Firefox does not open, but instead gives the error message, "Failed to read the configuration file." It has worked in the past, but not now.

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Firefox does not open, but instead gives the error message, "Failed to read the configuration file." It has worked in the past, but not now.

We recently uninstalled a proxy website's filtering program. Now, Firefox will not open, but instead, gives the error message, "Failed to read the configuration file. Please contact your system administrator." I've reinstalled it with a reboot between uninstalling and reinstalling. That didn't work. I installed a previous version, that didn't work. Finally, I reinstalled it without keeping any of my settings and bookmarks and it still doesn't work. I've checked my firewall and it's in the exceptions. Deleted that and replaced it. All to no avail. Still scratching my head.

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Site Moderator

Re: Firefox does not open, but instead gives the error message, "Failed to read the configuration file." It has worked in the past, but not now.

You get that error if a mozilla.cfg file is specified, but can't be processed or isn't found.
So it must at least be specified to get that error.


Try to delete the Firefox program folder before reinstalling Firefox to be sure that all files are removed.

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

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

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.


6 REPLIES
Shooting Star Contributor

Re: Firefox does not open, but instead gives the error message, "Failed to read the configuration file." It has worked in the past, but not now.

Hi,

Please check if there's a mozilla.cfg file in the Firefox installation folder and rename or delete it, if present.

...............................................................................................................................

Useful links:

All about Tools > Options

Going beyond Tools > Options - about:config

about:config Entries

Page Info Tools (Alt + T) > Page Info, Right-click > View Page Info

Keyboard Shortcuts

Viewing Video without Plugins

Firefox Profile Folder & Files

Firefox Commands

Basic Troubleshooting

After Upgrading

Safe Mode

Problematic Extensions

Troubleshooting Extensions and Themes

Troubleshooting Plugins

Testing Plugins

Site Moderator

Re: Firefox does not open, but instead gives the error message, "Failed to read the configuration file." It has worked in the past, but not now.

Deleting mozilla.cfg won't help. You need to remove the file that specifies to use mozilla.cfg. That is probably a file in the defaults\pref folder (C:\Program Files\Mozilla Firefox\defaults\pref)

See http://kb.mozillazine.org/Locking_preferences

Shooting Star Contributor

Re: Firefox does not open, but instead gives the error message, "Failed to read the configuration file." It has worked in the past, but not now.

co-rel is right, the file to be renamed / deleted is local-settings.js file, if present in the \defaults\pref folder which points to mozilla.cfg.

New Contributor

Re: Firefox does not open, but instead gives the error message, "Failed to read the configuration file." It has worked in the past, but not now.

Thanks guys, but neither of these files exist.

Site Moderator

Re: Firefox does not open, but instead gives the error message, "Failed to read the configuration file." It has worked in the past, but not now.

You get that error if a mozilla.cfg file is specified, but can't be processed or isn't found.
So it must at least be specified to get that error.


Try to delete the Firefox program folder before reinstalling Firefox to be sure that all files are removed.

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

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

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.


New Contributor

Re: Firefox does not open, but instead gives the error message, "Failed to read the configuration file." It has worked in the past, but not now.

Jalapeno! Finally. Something that works. I never thought to check to see if the folder was still there after uninstalling or that there may be hidden files left behind.

Thanks Cor-el