Ensure that your system's time is configured correctly because incorrect times can create some conflicts when it comes to internet certificates.

You can also view this Mozilla support article for some more information on the issue and some other steps that may help to solve your issue:

• What do the security warning codes mean?

I've checked my time, did all the stuff it says about my antivirus. no joy

It could be possible that an addon that is installed on your Firefox browser is causing the issue.

To see if this is the issue, please run Firefox in Safe Mode. Safe mode is a diagnostic mode that will temporarily disable your addons, hardware acceleration and some of your settings. If the issue is not present in safe mode, this issue is probably caused by an addon.

For more information on using Firefox Safe Mode, please refer to this Mozilla support article:

• Use Troubleshoot Mode in Firefox

I tried that, as well as refreshing Firefox. Still doesn't work

It's possible that some malware installed on your system may be causing the issue and potentially attempting to direct you to an illegitimate version of the website in order to steal your credentials or gather information.

You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• MalwareBytes' Anti-Malware
• Anti-Rootkit Utility - TDSSKiller
• AdwCleaner (for more info, see this alternate AdwCleaner download page)
• Hitman Pro
• ESET Online Scanner

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one. Windows 8 has antivirus built-in already.

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

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