The difference between the two is not as intuitive as it might seem. User interface: the language in which you want to see the browser (menus, preferences, etc.).Technically, this is done by sending an Accept-Language HTTP header, which contains a list of locale codes in the user’s preferred order. Web content: when you visit a web page, the browser will communicate to the server which languages you’d like to see content in.
In Firefox there are two main user facing settings related to languages:
