https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

Note: Some software, like Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

Is this about the language in the user interface?

Hi again,

if I change the language (pic 1) and I go to my Mozilla user bar (right above) than the just changed new language returnes to the old one (pic 2).

Thank you.

What language version do you have installed and what is the value of the general.useragent.locale pref on the about:config page?

Your screenshot shows a Dutch version for the user interface. When you open a specific page via a link that includes the language like 'de' in the first screenshot then you will (should) always get the page in that German (de) language.

If the Firefox user interface (toolbars) is in the wrong language or if you want to change the current language then you can get Firefox in the language of your choice via this page.

• https://www.mozilla.org/en-US/firefox/all/