Firefox sends your preferred language/locale with each request; you can control that. However, some websites may use location information, based on your IP address, to serve you a different language. To override that you would need to find a setting on the website.

Firefox's Language Setting

Open the Options/Preferences page:

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

In the search box at the top of the page ("Find in Options"), type lang and Firefox should filter to the "Choose" button in the Language section. Go ahead and click that. Here you can set the language codes Firefox sends with web requests.

(In Firefox 55 and earlier there's no search box; click Content in the left column to access the setting.)

Does that help?

You can use websites like these to see how your location is reported via a reverse DNS look up of your IP:

• http://whatismyipaddress.com/
• http://www.yougetsignal.com/tools/network-location/