Error loading websites
This article offers solutions to errors you may receive in Firefox or Mozilla Suite/SeaMonkey when attempting to connect to some or all websites. Error messages may include "The document contains no data" and "The connection was refused when attempting to contact..." or an error page may tell you that the server could not be found or that the connection has timed out.
If you can't get any website to load immediately after updating your browser, it is almost certainly your firewall or other security software blocking the connection.
Error loading any website
If Firefox/Mozilla Suite/SeaMonkey will not connect to any website:
- As with anything else, the problem may go away once you reboot your system.
- Make sure you are connected to the Internet. If you use dial-up and want your Mozilla application to automatically connect when you start it, see Autoconnect.
- Make sure that File -> Work Offline is not checked.
For specific connection or page load issues, see the section below that best describes your problem.
Only Mozilla applications are having problems
If your Mozilla application can't connect to websites but other programs such as Internet Explorer can...
Make sure your connection settings are correct. If you have Internet Explorer and it works, compare Internet Explorer's connection settings (e.g., Control Panel -> Internet Options -> Connections: LAN) to those of Firefox (Tools -> Options -> Advanced -> Network / Connection -> Settings) or Mozilla Suite/SeaMonkey (Edit -> Preferences -> Advanced -> Proxies).
If your connection settings are not correct but any changes you try to make are not saved after restarting your Mozilla application, make sure you don't have a utility program such as "Hide IP Platinum" that modifies your connection settings. Even if the utility is no longer installed, the user.js file may still contain the modified settings . To resolve this problem, open the profile folder and look for a user.js file. If found, either remove the user.js file or edit it to remove any "proxy" settings it may contain as outlined here, then reset the connection settings.
Another possible solution reported by a user who had recently removed "HideMyIP Premium" from his computer, was to reinstall the program and de-select the service. 
Make sure that your firewall program is configured to allow internet access to Firefox/Mozilla Suite/SeaMonkey. The Firewalls article includes configuration information on some of the more popular software firewalls.
Most firewalls will ask you whether to allow a new program to connect to the internet, so it is important to always allow access for new or updated Mozilla applications. Even if you see permission in the firewall list of permitted programs, it could be for the previous program version, as firewalls require permission to allow an updated program to access the internet .
Some firewalls can be rather tricky to configure, or even to disable or uninstall. In some cases they may continue running silently after supposedly being uninstalled or disabled. They may also have bugs that prevent the Internet access list from being updated correctly. The "EnumProcess" tool for Windows, available here, enumerates all running processes and identifies firewall processes. It also identifies some of the other security programs (but not necessarily all) that are known to cause problems.
Firewalls have many ways of blocking Internet access. Some firewalls and other security software manage all aspects of Internet connections and Web traffic, including domain-name service (DNS), access to secure Web sites, and browser access to your computer. Kaspersky software can block domain-name service (DNS) for some programs but not others.  You must allow DNS access for normal Web browsing.
Other security programs
Besides personal firewalls, other security programs, including Norton or Symantec Antivirus,   can block internet access or cause other connection issues, especially after the browser is updated. Older versions of Panda Anti-virus can cause connection problems. (Information on this is no longer available on the Pandasoft Web site.)
Note that some antivirus packages include web scanning features, such as AVG v9's "Link Scanner", Avast! "Web Shield" and Kaspersky "Web Anti-Virus", that process all HTTP traffic, which may cause intermittent timeouts and failed page loads (see below, under Websites randomly do not load) .
Http and P2P blocking software, such as Peerguardian or Peerblock may block websites from loading if their IP happens to appear on a block list. As with other security programs disabling it while you diagnose networking issues is advisable.
By default, Firefox/Mozilla Suite/SeaMonkey will use IPv6 ("Internet Protocol version 6") if it is available. However, the user's local network or Internet environment may not be equipped to handle IPv6 and you may see an "Address not found" or "Server not found" error for many websites. (Read bug 414197 and this forum discussion for examples.)
To disable IPv6, change the preference network.dns.disableIPv6 from "false" to true . Here are the steps:
- Type about:config in the address bar, press Enter.
- Find network.dns.disableIPv6 in the list.
- Right-click -> Toggle.
- Restart your Mozilla application and try again.
If this doesn't work, you can re-enable IPv6 by resetting the preference to "false" (double-click to toggle).
DNS prefetching is performed to resolve domain names to IP addresses while loading web pages. If a page includes links, images, or other content from different domains, multiple DNS requests will be made at once. This may break the DNS forwarder in several different routers and you may see "Server not found" errors for many websites.   To disable DNS prefetching, create a new boolean preference named network.dns.disablePrefetch in about:config and set it to true, as follows:
- Type about:config in the address bar, press Enter.
- Context click (right-click) in the preferences list and select "New -> Boolean".
- Type or paste in the preference name network.dns.disablePrefetch and click OK.
- Select true as the value and click OK.
If this doesn't help you can re-enable DNS prefetching by resetting the preference to "false" (double-click to toggle).
Accessing a router
All programs are having problems
Diagnosing Windows network connections
For help with network and Internet connections read this Microsoft article: "How to troubleshoot TCP/IP connectivity with Windows XP". There is also a Windows 2000 version of the article. Much of the article is also applicable to other operating systems, with some variations.
Most routers can be configured with rather complex Internet access restrictions. For example, specific Websites can be blocked, and specific computers can be blocked at certain times of the day. Access to HTTP sites or HTTPS (secure) sites can be blocked. Access to certain services such as domain-name resolution (which is required for normal browsing) can also be blocked.
In combination, the rules could also appear to be erratic. For example, if access were determined by IP address, the rules might appear to change when IP addresses change.
For help with router configuration, contact your system administrator or refer to your router's documentation. If possible, see if you can connect without hooking up to the router.
Viewing system logs
System event logs may contain information on important events such as service failures, and application updates and failures. For an example of an Internet service interruption, read this. To view the Windows Event Viewer, Start > Run > eventvwr.
If your domain name system server (DNS server) becomes slow, you may be unable to view some or all websites. There is a good explanation here of how the DNS system works and what can go wrong with it. Your DNS server translates web addresses (URLs) that you enter in your browser, into IP addresses that are used on the Internet. If you can open a website by entering the IP address into the Location Bar but not the URL. For example, if an IP address for Google such as http://184.108.40.206/ or http://220.127.116.11/ works but http://www.google.com doesn't, you may have a DNS problem.
Google has provided a very good guide to configuring and diagnosing DNS. You can also check the speed of your DNS server by downloading the "wdnslookup" utility for Windows, available here, or by using program "nslookup", which is part of most operating systems. Remember that both local DNS servers and your own computer cache the results, so a lookup may be much slower on the first attempt. For accurate results you should use the "Clear Cache" button in the wdnslookup utility before resolving the host name you enter. This will clear the DNS cache in your computer, but not the server cache. See this forum post for additional information.
As a first step toward fixing the problem, you should contact your ISP. You can also use an alternative service such as OpenDNS (discussed here), Google Public DNS, or TreeWalk. Other ways to find a more reliable service are discussed here. In some cases replacing your DNS may result in a dramatic, general improvement in Internet speed. As a last resort, it may help to increase the DNS query timeout for the operating system, although this will not result in any improvement in speed. Directions for Windows 2000 are shown here.
A related DNS server issue that can result in failure of repeated attempts to open certain websites is that Windows 2000 and XP cache unsuccessful DNS lookup attempts. This means that you may not be able to view a particular website until the cached result expires. By default, the expiration time is 5 minutes. As a workaround, you can flush the DNS cache (For Windows XP, "Start -> Run -> ipconfig /flushdns") then try loading the site again. If you want, you can permanently disable negative caching by editing the registry, as shown here. The registry entry is officially documented here (Windows 2000) and here (Windows XP).
Usually if Firefox is having DNS problems, other programs such as nslookup and other Web browsers will also have the same problem, but this is not always the case. A setup with an incorrect address for the DNS service can cause systemic delays for Firefox in some cases. Security software can also block DNS service for Firefox.
Are others also experiencing problems
You can check if the problem is global in nature by seeing if another server can see it
- Check url availability with DOJ.me | Down Or Just Me | Is It Down, the site will check the url availability for you and also provides a bookmarklet that you use from the failed page to check its availability. Perhaps assign a keyword shortcut to it of "up:down" to make it easier to invoke.
Some server health reports for sites that would affect all MozillaZine users.
- for mozilla servers, Public Website Health Status for Mozilla provides "Current Performance and Availability Status" and you can scroll down to "Performance and Availability History" for earlier reports.
- (need similar reports for mozillazine.org and for google.com)
If programs other than Firefox/Mozilla Suite/SeaMonkey are also having problems connecting, the problem may be with your Internet Service Provider. Contact them.
Spyware and other malware
It is possible that Spyware or other malware (malicious software) is causing connection problems. Your antivirus and security software may not detect the malware so you should install and run another anti-malware application or visit a forum that specializes in detecting and removing malicious software from your computer. Some recommended applications and forums are listed here.
Error loading some websites
If Firefox or Mozilla Suite/SeaMonkey can connect to some websites, but not others:
- If you receive an error message from a website, the error message may be cached. Attempts to reload the site may yield only the cached error message. To force a reload from the Internet, hold down the <Shift> key and press the Reload button. 
- Clear the browser cache:
- Message: "firefox can't find the file at", even though the file actually exists. Since the message comes up in a pop-up there is no chance to retry with Ctrl+F5 (Cmd+Shift+R on Mac) to reload bypassing cache; solution: clear cache as described immediately above.
- Delete any stored cookies for the problem site and also make sure that cookies from the website are not being blocked.
- Temporarily turn off ad-blocking. Extensions and Internet security software that block advertising or other unwanted content can cause problems loading webpage content; you may see an error message, The connection to the server was reset while the page was loading.  (Note that some ad-blocking software add entries to the hosts file that can also cause this error.) You may be able to determine that part of the site has been loaded by selecting "View > Page Source" from the menu.
- A hosts file contains a mapping of host names to IP addresses and has the ability to redirect Internet requests in all browsers. If you are getting connection errors for certain websites (e.g., "Failed to connect" or "Unable to connect") you should look for a hosts file and review its contents for entries other than
127.0.0.1 localhost. 
- Try disabling IPv6 (see above).
- Try disabling DNS prefetching (see above).
- If repeated attempts fail to open a website, Windows may have cached an unsuccessful DNS lookup attempt. This means that you may not be able to view a particular website until the cached result expires. As a workaround, you can flush the DNS cache (On Windows XP: "Start -> Run -> ipconfig /flushdns") then try loading the site again. See this discussion and this example.
- If only web pages with IP-addresses beginning with one particular number won't load, then there may well be a problem with the subnetmask in the router. Check by sending a ping. Pings to all addresses beginning with this number will get lost, while others don't. Define the subnetmask more precisely. This has solved elusive problems more than once. An example of what has actually worked: IP-address: 85.x.x.x. Subnetmask that didn't work: 255.0.0.0. Subnetmask in the router that has solved the problem: 255.255.255.248.
- The website may have blocked your IP address or a range of addresses that includes yours. If you suspect this might the case, contact the webmaster.
- If you enabled network.http.pipelining (a "tweak" designed to improve page loading time), disable it in about:config by typing "pipelining" in the filter, right-clicking all entries, and choosing "Reset". (Also remove the associated entry in the user.js file, if it exists.)
- If the website is a secure site such as a bank, Paypal, eBay, or any site that begins with "https:", see Error loading secure sites.
- If you receive one of these errors when loading certain sites, see the related article:
- This object has been blocked.
- SSL protocol has been disabled
- Cannot connect securely because the site uses an older insecure version of the SSL protocol
- Could not initialize the browser security component
- OCSP error when accessing secure sites
- Unresponsive Script Warning
- The page is not redirecting properly
- You may be infected with spyware or other malware that can cause search engines to fail, redirect you to unwanted websites, or prevent certain websites from loading.  Scan your system with something other than your normal security software or visit a forum specializing in malware removal (recommendations are listed here).
- The Outpost Pro Firewall can sometimes interfere with loading certain sites. ,
- The website may only allow Internet Explorer users. You can work around this problem by installing a user agent spoofer, such as the User Agent Switcher extension, to make the website think you are using a different browser.
- Make sure you've entered the correct address.
- Try loading the same website from another computer or browser; if it still doesn't load, the problem is likely with the website.
Websites randomly do not load
If Firefox or Mozilla Suite/SeaMonkey randomly cannot connect to websites:
- The site may be down or experiencing difficulties. Try loading the site from another computer or browser to see if this is the case.
- Intermittent timeouts and failed page loads can be caused by web scanners bundled with certain anti-virus packages that process all HTTP traffic, such as Kaspersky "Web Anti-Virus" and Avast! "Web Shield". (Avast users have reported the error, Connection Interrupted. The connection to the server was reset while the page was loading.) In such cases,
- If you are using the Comodo firewall, it can cause a conflict with your antivirus scanner and interfere with file downloads. Try updating Comodo to the latest version. See this forum thread for details.
- Try modifying network.http.max-connections in about:config to a lower value such as 48, or 30 which was the previous default before it was increased to 256. Note: this issue should be fixed in Firefox 8.   
- If you enabled network.http.pipelining (a "tweak" designed to improve page loading time), disable it in about:config by typing "pipelining" in the filter and right-clicking all entries and choosing Reset. (If you set this preference by editing the "user.js" file, remove this edit.)
- You may have problems with your domain name service (DNS).
- Sometimes when you first try to use the Internet, your computer may take some time, perhaps up to a minute, to establish a connection. In this case, whichever application is first to use the Internet may experience temporary difficulty, but once a connection is established, all programs should work correctly.
- Try disabling IPv6 (see above).
- Problematic extensions can cause problems loading web pages (see the linked article for specifics). Try updating all extensions to the latest version first, then disable your extensions or try Safe Mode. Examples of problematic extensions:
- The Skype Extension for Firefox may cause pages to continually reload or stop loading 
- The DownThemAll extension can cause random pages or all pages to stop loading (Note that DownThemAll 1.0 changes certain "network.http" preferences that must be reset, even if you disable or uninstall the extension.)
- If the above doesn't help, perform the full Standard diagnostic.
- Websites look wrong
- Browser attempts to connect when already connected
- Images or animations do not load
- Firefox/Projects/Network Error Pages #References at wiki.mozilla.org
- Why can't I connect to Google? How do I fix this?
- Error loading web sites (Firefox Support)