This usually happens when Facebook is detecting a different language preference (or region setting) from your browser/session, rather than a Firefox “problem” itself. Here are some practical steps to fix it: 1. Change Facebook language manually (most important) Even if the interface is in Japanese, try: Scroll to the bottom of the page Look for a language option (it may show as 日本語) Change it to English (US) / English (UK) If you can’t find it easily, try this direct link after login: https://www.facebook.com/settings?tab=language 2. Force English via URL (quick workaround) Try opening Facebook like this: https://www.facebook.com/?locale=en_US This often overrides the default language temporarily. 3. Check Firefox language settings Sometimes Firefox sends a language preference to websites. Go to Settings → General → Language Set preferred language to English (US) Remove or move Japanese below English if it exists Then restart Firefox. 4. Clear cookies for Facebook If Facebook saved a Japanese preference: Open Firefox settings Privacy & Security → Cookies and Site Data Search “facebook.com” Remove cookies/cache for Facebook Log in again 5. Disable VPN / location-based mismatch (if any) If you are using: VPN Proxy Or a region-based extension Facebook may auto-load Japanese based on detected region. Try turning it off and reload Facebook. 6. Check Facebook account language (permanent fix) Once you regain access: Settings & privacy → Settings Language and region Set Display Language to English