Bonjour. You can check in the profile folder if you have a user.js file that sets this pref to false. The user.js file will only be present if you or other software has created this file and normally won't be present. You can check its content with a text editor (right-click: "Open with"; do not double-click). The user.js file is read each time Firefox is started and initializes preferences to the value specified in this file, so preferences set via user.js can only be changed temporarily for the current session. You can delete the user.js file if you didn't create this file yourself. You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the <b>about:profiles</b> page. *Help -> Troubleshooting Information -> Profile Folder/Directory:<br>Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder *https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data See also: *https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

ça marche ! It works ! Thanks