Fix slowness, crashing, error messages and other problems - Server Not Found - Troubleshoot connection problems

If you have a problem connecting to a website, you may see error messages like Server Not Found. This article describes how to troubleshoot problems that cause this error.

• For troubleshooting other error messages, see Error loading websites. 

Try another browser

To begin, try opening a website in another browser (such as Internet Explorer).

• If all other browsers cannot load the website, move on to the No browsers can load websites section.
• If the other browsers can load the website, skip ahead to the Firefox cannot load websites but other browsers can section.

No browsers can load websites

If neither Firefox nor your other browser can load websites, your problem is not in Firefox, so you should seek help elsewhere, for example, at Microsoft.com:

• (Windows 10): See Why can't I get online?
• (Windows 8): See Why can't I connect to the Internet?
• (Windows 7): See Why can't I connect to the Internet?
• (Windows Vista): See Troubleshoot Internet connection problems
• (Windows XP): See How to troubleshoot possible causes of Internet connection problems in Windows XP

You should also check the following:

• Make sure your modem and/or router are both on and are not indicating errors.
• If you are using a wireless connection, make sure that you are connected to the right access point.
• Make sure your Internet security software (including firewalls, antivirus programs, anti-spyware programs, and more) is not blocking connections to the Internet. For instructions on how to configure these programs, see the Configure firewalls so that Firefox can access the Internet article.
• If you use a proxy server, make sure that the proxy server can connect to the Internet. For instructions on configuring proxy settings in Firefox, see Firefox connection settings below.

Firefox cannot load websites but other browsers can

If Firefox cannot load websites, but your other browser can, follow the instructions below.

Cannot load websites after updating Firefox

If you were able to load websites until you updated Firefox, your Internet security software (including firewalls, antivirus programs, anti-spyware programs, and more) is likely preventing Firefox from connecting to the Internet. Some Internet security programs can block Internet access even when they are in a "disabled" state.
In general, you should remove Firefox from your program's list of trusted or recognized programs, then add it back. For instructions on how to configure these programs, see the Configure firewalls so that Firefox can access the Internet article.

Firefox connection settings

If you connect to the Internet through a proxy server that is having connection problems, you will not be able to load websites. To check your Firefox proxy settings:

1. Click the menu button and choose Options.
2. Select the Advanced panel.
3. Select the Network tab.
4. In the Connection section, click Settings....
5. Change your proxy settings:
   • If you don't connect to the Internet through a proxy (or don't know whether you connect through a proxy), select No Proxy.
   • If you connect to the Internet through a proxy, compare Firefox's settings to another browser's (such as Internet Explorer - see Microsoft's guide to proxy settings).
6. Click OK to close the Connection Settings window.
7. Close the about:preferences page. Any changes you've made will automatically be saved.
   

DNS Prefetching

DNS Prefetching is a technique Firefox uses to speed up loading new websites. To disable DNS Prefetching:

1. In the Location bar, type about:config and press Enter.
   
   • The about:config "This might void your warranty!" warning page may appear. Click I'll be careful, I promise! to continue to the about:config page.
2. Right-click in the list of preferences, select New, and then select Boolean.
3. In the Enter the preference name window, enter network.dns.disablePrefetch and click OK.
4. Select true when prompted to set the value and click OK.

IPv6

Firefox supports IPv6 by default, which may cause connection problems on certain systems. To disable IPv6 in Firefox:

1. In the Location bar, type about:config and press Enter.
   
   • The about:config "This might void your warranty!" warning page may appear. Click I'll be careful, I promise! to continue to the about:config page.
2. In the Search field, type network.dns.disableIPv6
3. In the list of preferences, double-click network.dns.disableIPv6 to change its value from false to true.

Firefox cannot load certain websites

If you find that Firefox can load some websites but not others, first clear your Firefox cookies and cache:

1. Click the menu button , choose History and select Clear Recent History....
2. In the Time Range to clear: drop-down, select Everything.
3. Click the arrow next to Details to display the list of items that can be cleared.
4. Select both Cookies and Cache.
5. Click Clear Now.

Check for malware

If clearing your cookies and cache did not enable you to load the websites that did not work in Firefox, you should check your computer for malware. Certain types of malware are known to target Firefox and can prevent it from loading various websites:

• If you have an antivirus or Internet security program, update its detections database and do a full scan of your system.
• If you still have problems, see How do I get rid of malware?