Unable to open Firefox, configuration file read failure.

Hello,

Uninstall and reinstall properly.

Recover your bookmarks:

Open Firefox,
Bookmarks
Show All Bookmarks
Import and Backup
Export to HTML format...

Save the file to the desktop.

Backup your important data to the desktop:

The files places.sqlite, key3.db, permissions.sqlite, etc.....

==> https://support.mozilla.org/fr/kb/recuperer-donnees-importantes-ancien-profil?esab=a&s=profil&r=2&as=s#w_vos-donnaees-importantes-et-leurs-fichiers

Start Menu
Control Panel
Programs and Features (for Windows Vista/Seven)
Add or Remove Programs (for Windows XP)
Uninstall Firefox

Agree to uninstall everything
Check "Remove all my files"

Restart the PC.

Go to: C:\program files or C:\Programs
Delete the folder "Mozilla Firefox" (If it exists)

Install and run CCleaner for cleanup in Windows, applications, and registry.

Follow this tutorial

Install Firefox

Recover bookmarks:

Open Firefox
Bookmarks
Show All Bookmarks
Import and Backup
Import from HTML format....
Next

Go to desktop
Select "bookmarkbackups.html"

To recover your important data:

Place the various backed-up files from the desktop into the new profile created by Firefox.

Click on the Start button of Windows and select Run....

Type in the field

%APPDATA%\Mozilla\Firefox\Profiles\

Click on OK.

Windows Explorer opens the Profiles folder, which contains a folder for each profile.

Restart Firefox.

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In this world that turns out to be hot, every fox carries its tail in its own way.

Great, I completed all the steps and it's back on track. A big thank you.

For my personal knowledge, do you know where this problem came from?

Re,

You're welcome.

You probably had a configuration file issue in your Firefox profile folder.

--
In this world that turns out to be hot, every fox carries its tail in its own way.