Firefox Edge Browser Error Code NS_ERROR_UNKNOWN_HOST: How to Fix It

Easy 10-30 minutes Medium Severity Verified June 2026
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Error Code
NS_ERROR_UNKNOWN_HOST
Brand
Firefox Edge
Product Type
browser
Severity
Medium
DIY Difficulty
Easy
Estimated Fix Time
10-30 minutes
The NS_ERROR_UNKNOWN_HOST error in Firefox means the browser cannot find or resolve the domain name (hostname) of the website you are trying to visit. This typically happens when there is a DNS (Domain Name System) issue, a network connectivity problem, or a misconfigured browser or system setting. The good news is that in most cases this error can be resolved at home without any technical expertise by following a few straightforward troubleshooting steps.
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Tools You'll Need

How to Fix Error Code NS_ERROR_UNKNOWN_HOST

  1. Check Your Internet Connection

  2. Reload the Page and Try a Different Browser

  3. Flush Your DNS Cache

  4. Change Your DNS Server

  5. Disable Firefox DNS over HTTPS (DoH) or Change DoH Provider

  6. Clear Firefox Cache and Cookies

    Clearing cookies will log you out of all websites. Make sure you know your login credentials before proceeding.

  7. Disable VPN, Proxy, or Firewall Temporarily

    Only disable your firewall or antivirus temporarily for testing purposes. Re-enable it immediately after your test to keep your device protected.

  8. Check and Edit the Hosts File

    Be careful editing the hosts file. Only remove entries you are certain are incorrect. Editing other entries can break other websites or system functions.

  9. Reset Firefox Network Settings or Refresh Firefox

    Refreshing Firefox will remove installed extensions, themes, and modified preferences. Your bookmarks, saved passwords, and browsing history will be preserved.

  10. Update Firefox and Your Operating System

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When to Call a Professional

If you have tried all the steps above and the error persists only for specific websites while others load fine, the issue may be on the website's server side and nothing you can fix locally. Contact your Internet Service Provider (ISP) if no websites load at all after following these steps, as your ISP's DNS servers may be down or your account may have a connectivity issue. If you suspect your computer has been compromised by malware that is redirecting DNS queries, run a full malware scan using reputable security software or consult a professional IT technician.

Frequently Asked Questions

What does NS_ERROR_UNKNOWN_HOST mean in Firefox?
NS_ERROR_UNKNOWN_HOST means Firefox was unable to find the IP address associated with the domain name (hostname) you entered. This is essentially a DNS resolution failure — Firefox knows you want to visit a website, but it cannot translate the website's name into a network address to connect to it. Common causes include DNS server issues, internet connectivity problems, incorrect browser or system settings, or a corrupted DNS cache.
Why does NS_ERROR_UNKNOWN_HOST only happen on some websites and not others?
If only specific websites trigger this error, the most likely cause is either a stale DNS cache entry for that particular domain, a block in your hosts file, a firewall or parental control rule targeting that site, or an actual DNS propagation issue on the website's end. Try flushing your DNS cache and checking your hosts file for any entries related to the affected domain. If the site is newly launched or recently changed domains, you may need to wait a few hours for DNS propagation to complete.
Does NS_ERROR_UNKNOWN_HOST mean the website is down?
Not necessarily. While a website being down or having DNS configuration problems on their server can cause this error, the majority of NS_ERROR_UNKNOWN_HOST errors are caused by local issues on your computer or network. Try visiting the website in a different browser or on a different device connected to the same network. You can also use a website status checker such as downforeveryoneorjustme.com to see if the site is globally unavailable.
Will clearing Firefox cache fix NS_ERROR_UNKNOWN_HOST?
Clearing the Firefox cache can help in some cases, especially if a corrupted cache entry is causing the DNS lookup to fail. However, since this error is primarily a DNS resolution problem, flushing your system's DNS cache using Command Prompt or Terminal is often more effective. For best results, try both: flush the system DNS cache and clear the Firefox browser cache.
Can a VPN cause NS_ERROR_UNKNOWN_HOST in Firefox?
Yes, a VPN can cause this error. When a VPN is active, your DNS queries are routed through the VPN's servers. If those servers are slow, misconfigured, or experiencing an outage, DNS resolution can fail and trigger NS_ERROR_UNKNOWN_HOST. Try temporarily disabling your VPN and reloading the page. If it works without the VPN, contact your VPN provider's support team or try switching to a different VPN server location.

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