Websites randomly don't load

This article is about Firefox/Mozilla Suite randomly having problems connecting to or loading websites.
If Firefox/Mozilla Suite has problems loading any website, read Error loading any website.
If Firefox/Mozilla Suite can successfully load some websites but not others, read Error loading some websites.

• Clear your Cache: "Tools -> Options -> Privacy -> Cache -> Clear Cache Now"
• The site may be down or experiencing difficulties. Try loading the site from another computer or browser to see if this is the case.
• 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.
• To determine if an extension is the cause of your problems try Safe_Mode. If that doesn't help, perform the full Standard_diagnostic_(Firefox).
• If the previous points didn't help or don't apply, try the other articles in Error loading websites.