Regarding language, I'm going to guess that you downloaded a localized build that set that locale as the preferred language, or that it is coming from your OS: https://support.mozilla.org/en-US/questions/949545
Chrome has this also: https://support.google.com/chrome/answer/173424?hl=en
Suggesting an "underhanded user-memory choice" is a serious claim. It might be worth comparing your browsers' language settings.