Hi Fury_Phoenix, thank you for that certificate. It says it was issued by "Microsoft Family Safety" which is a parental control feature/app for Windows.

If you are the boss of the computer and shouldn't be subject to parental controls, you could check the settings for that program and make sure you aren't in a group. (I think. Haven't looked at it for a long time and don't have a link handy about how to do that.)

If you aren't running Microsoft Family Safety, it's possible another program has used that certificate for its own nefarious purposes. You may want to do some malware scanning. See:

Troubleshoot Firefox issues caused by malware

But it was set to allow all sites

Hmm, the certificate error doesn't mean the sites are blocked, but it's weird that the error only appears for those sites and not other HTTPS addresses.

If you trust the intermediary to read and modify your browsing, you could consider this settings change and see whether it makes any difference:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

(2) In the search box above the list, type or paste enterp and pause while the list is filtered

(3) Double-click the security.enterprise_roots.enabled preference to switch the value from false to true

That sets Firefox to trust the certificate stored at the system level, which are the certificates used by your other browsers. This makes Firefox a little less resistant to hijacks, so you should continue to limit program installs to trusted programs.

But it is a trusted program that built in. Why would it block a search engine for?

Fury_Phoenix said

But it is a trusted program that built in. Why would it block a search engine for?

I don't know what you mean. If Microsoft Family Safety inserts itself in your browsing and generates fake site certificates so it can read what you're searching about, Firefox will object to those certificates because Microsoft Family Safety is not trusted to issue certificates for those sites. That's why you have to do extra setup if you want to use a "man in the middle."

Oh I get it. So it is making it own certificates which is why it is being rejected. Thanks for explaining it to me. I will try it and see how it goes

Odd. It is locked and set to true already.

Hmm, maybe the duplicate certificate is in the Windows certificate store. I am not familiar with how to delete old site/server certs from there, but presumably there's a control panel?

And how would i delete it? And will Family Safety from Microsoft regenerate the certificates?

Sorry, I thought yours was the thread with the duplicate serial number error code.

Which error code are you getting? It typically looks like SEC_ERROR_SOMETHING.

And it's only for major search sites?

Locking the certificate store to the system store is something that security software might do (e.g., Avast/AVG) to reduce certificate errors. I suppose there could be other explanations for that.

It fixed itself. Anyway, yes it was SEC_ERROR_SOMETHING (can't remember). It was for only search sites. And it fixed itself a day later.

Note that on Windows 8.1 Firefox can import MS Family certificates automatically.

• security.family_safety.mode = 2
• https://dxr.mozilla.org/mozilla-release/source/security/manager/ssl/nsNSSComponent.cpp#449

And how would I do that?