when Firefox cannot load websites, but other web browsers (such as Google Chrome) can, Firefox may show a Server not found or Unable to connect error message.

Try this:

To disable IPv6 in Firefox:

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.

In the Search field, type network.dns.disableIPv6.

In the list of preferences, double-click network.dns.disableIPv6 to set its value to true.

That could be a problem with the usage of libPKIX in the Firefox 31 and later releases.

• https://blog.mozilla.org/security/2014/04/24/exciting-updates-to-certificate-verification-in-gecko/

It is possible to disable this new feature by disabling libPKIX support, but this is not recommended for security and vulnerability reasons.

• about:config page: security.use_mozillapkix_verification = false

It is possible that the website will fix this issue shortly, so make sure to check regularly if this workaround is still required by resetting the pref and see if it works. You may have to reload and bypass the cache via Ctrl+F5.

You can contact the website and bring this article under their attention: Behavior Changes and Things for CAs to Fix:

• https://wiki.mozilla.org/SecurityEngineering/mozpkix-testing