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Address lookup (DNS) errors

Firefox: Hmm. We're having trouble finding that site.

Firefox could not find the address for this website name.

Quick answer

This is Firefox's message for a failed address (DNS) lookup. The name may be mistyped, the site may have no working address records, or your connection, proxy or security software may block the lookup.

When to wait: Rarely; check the address and connection first.

If you are visiting the website

  1. Check the address Look for typos in the web address, such as a missing letter or the wrong ending (.com instead of .de).
  2. Try another browser Open the same address in Chrome, Edge or Safari. If it works there, the cause is a Firefox setting or add-on, so continue with the Firefox steps below.
  3. Check Firefox's proxy setting A leftover proxy (a middleman server for web traffic) makes every lookup fail in Firefox only.
    Windows
    Open Firefox Settings, search for Network Settings and click Settings. If you do not use a proxy, choose No proxy or Use system proxy settings, then click OK.
    macOS
    Open Firefox Settings, search for Network Settings and click Settings. If you do not use a proxy, choose No proxy or Use system proxy settings, then click OK.
    Linux
    Open Firefox Settings, search for Network Settings and click Settings. If you do not use a proxy, choose No proxy or Use system proxy settings, then click OK.
  4. Clear Firefox's DNS cache Type about:networking#dns in the address bar, press Enter and click Clear DNS Cache. Then reload the page.
  5. Test DNS over HTTPS Firefox can use its own secure DNS service (DNS over HTTPS). If that service cannot be reached from your network, names fail only in Firefox. In Settings > Privacy & Security, find DNS over HTTPS, test with Off or Default Protection, then set it back the way you like it.
  6. Restart in Troubleshoot Mode Open the menu, choose Help > Troubleshoot Mode and click Restart. Add-ons are switched off temporarily; if the site loads now, turn your add-ons back on one at a time to find the cause.
  7. Clear the system DNS cache The operating system keeps its own lookup memory, which Firefox uses when secure DNS is off.
    Windows
    Open Command Prompt and run: ipconfig /flushdns.
    macOS
    In Terminal run: sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder.
    Linux
    On systems that use systemd-resolved, run: resolvectl flush-caches.
    Android
    Turn Airplane mode on and off again, or restart the phone.
  8. Restart your router Turn your router off, wait about 30 seconds and turn it on again. This renews your connection and its address lookup.

If you run the website

  1. Check DNS records Make sure the domain resolves to your server. Test from outside with dig example.com A +short or nslookup example.com 1.1.1.1.

Is it the website or me?

Open the address in another browser on the same computer. If it works there, the cause is inside Firefox: proxy, secure DNS or an add-on. If it fails everywhere, check your connection or the address itself.

How it differs from Chrome's ERR_NAME_NOT_RESOLVED

Both mean the website name could not be turned into an address. Firefox shows a friendly 'trouble finding that site' page instead of a code. The fixes are almost the same, plus Firefox's own proxy and DNS over HTTPS settings.

For developers: what happens technically

Firefox shows this page when its resolver returns no address for the host. With DNS over HTTPS on, Firefox may ask a different resolver than the operating system does. So dig on the same machine can succeed while Firefox fails, or the other way round.

Common questions

Why does only Firefox fail while Chrome works?

Firefox has its own proxy and secure DNS settings. If one of them points to a service that does not answer, only Firefox is affected. Set the proxy to No proxy or system settings and test DNS over HTTPS Off for a moment.

Is it safe to turn off DNS over HTTPS?

It is fine as a short test. Without it, your lookups go to your network's normal DNS service, as with most other apps. Turn it back on afterwards if you want the extra privacy.

Will clearing the Firefox DNS cache sign me out?

No. It only forgets remembered name lookups. Cookies, passwords and history are not touched.

What does Troubleshoot Mode change?

It temporarily turns off extensions, themes and some performance features. Nothing is deleted, and a normal restart brings everything back.

Likely causes

  • Common A typo in the address. (Your side)
  • Sometimes No internet connection or a DNS problem on your network. (Your side)
  • Sometimes A proxy or security software blocks Firefox. (Your side)
  • Sometimes The domain's DNS records are missing. (Website side)

Is the website down? Check it now

One measurement point. Results explain what we saw, not a worldwide verdict.

Sources

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