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. To make Firefox/Mozilla Suite autoconnect when it starts, see this article.
* Make sure that File -> Work Offline is not checked.
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Only Mozilla applications are having problems
If your Mozilla application can't connect but other programs such as Internet Explorer can...
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Connection settings
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 [1]. 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.
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Firewalls
Make sure that your firewall program is configured to allow internet access to Firefox/Mozilla Suite/SeaMonkey. 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 [2].
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. For more information on specific firewalls, see this article.
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. [3] You must allow DNS access for normal Web browsing.[4]
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Other security programs
Besides personal firewalls, other security programs, including Norton or Symantec Antivirus, [5] [6] 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 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) .
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IPv6
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. (Read this discussion for an example.) To disable IPv6, change the preference network.dns.disableIPv6 from "false" to true . Here are the steps:
1. Type about:config in the address bar, press Enter.
2. Find network.dns.disableIPv6 in the list.
3. Right-click -> Toggle.
4. Restart your Mozilla application and try again.
If this doesn't work, re-enable IPv6 by resetting the preference to "false".
