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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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  • Last reply by John99

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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.


I REINSTALL 10 TIMES SO DON'T TELL ME THAT!!! I'm piss because i need firefox working again so i can finish reseaching my speech in 5 days.

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. I REINSTALL 10 TIMES SO DON'T TELL ME THAT!!! I'm piss because i need firefox working again so i can finish reseaching my speech in 5 days.

Chosen solution

Yes, deleting Firefox program file.


Comment from moderator. Please see other posTs in this thread such as https://support.mozilla.org/en-US/que.../964939?page=3#answer-456928

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All Replies (20)

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Didn't HELP

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Which files do you have in the defaults\pref folder in the Firefox program folder?

  • (32 bit Windows) "C:\Program Files\Mozilla Firefox\"
  • (64 bit Windows) "C:\Program Files (x86)\Mozilla Firefox\"

See also "Other solutions":

Do a clean reinstall and delete the Firefox program folder before (re)installing a fresh copy of the current Firefox release.

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

Uninstall your current Firefox version, if possible, to cleanup the Windows registry and settings in security software.

  • Do NOT remove personal data when you uninstall your current Firefox version, because all profile folders will be removed and you lose 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.

  • (32 bit Windows) "C:\Program Files\Mozilla Firefox\"
  • (64 bit Windows) "C:\Program Files (x86)\Mozilla Firefox\"

Your bookmarks and other personal data are stored in the Firefox profile folder and won't be affected by an uninstall and (re)install, but make sure that "remove personal data" is NOT selected when you uninstall Firefox.


Modified by cor-el

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its say 86 but i think my computer is 32

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still not working

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Do you want to use a mozilla.cfg file (i.e. did you create this file yourself) to lock or set some preferences?

If the mozilla.cfg file in the main Firefox program folder is missing, but the .js file in defaults\pref is still present then you get this error message. It is also possible that there are other problems with this file.

If you have .js files apart from the channel-prefs.js file, that sets app.update.channel, in the defaults\pref folder then open this file in an editor like Notepad and please post its content.
Also please post the content of the mozilla.cfg file.

There shouldn't be a mozilla.fcg file present unless you've created it yourself to initialize some prefs.

If you have this mozilla.cfg file then best is to do a clean reinstall and delete the Firefox program folder before reinstalling a fresh copy of Firefox.

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i download something it lock me out of firefox. mozilla.cfg or .js files where do i find that at?

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I don't how to open firefox in notebook.

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You can do a clean reinstall like I posted above to remove this settings file.

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

  • (32 bit Windows) "C:\Program Files\Mozilla Firefox\"
  • (64 bit Windows) "C:\Program Files (x86)\Mozilla Firefox\"

You can find the full version of the latest Firefox 22.0 release in all languages and for all Operating Systems here:

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still not working

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help me stop telling me old things

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You won't be able to recover from this unless you remove the involved JavaScript and mozilla.cfg file, in case the latter is still there.

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Sorry you are still having a problem with Firefox.

This is a standard error and so we know what to expect normally causes it. Is there any possibility

  • You are failing to delete the correct folder when doing a clean install
  • You have security software that prevents deletion of certain Files, or is recreating them.

Suggestion next time you try a clean reinstall,

  1. Delete the Firefox program files
  2. Check that the files have been deleted
  3. Shut-down then reboot the computer (but do NOT re-install Firefox)
  4. Double check to ensure files are gone on restart.
  5. Only if the Files are not there re-install Firefox
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how do i uninstall Java?

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still not working

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did you follow cor-el instructions?

"You won't be able to recover from this unless you remove the involved JavaScript and mozilla.cfg file, in case the latter is still there."

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whats a clean reinstall?

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uninstall firefox then install it again from getfirefox.com

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i can't find javascipt

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