• MOZILLA_PKIX_ERROR_MITM_DETECTED
• uses an invalid security certificate SSL_ERROR_BAD_CERT_DOMAIN
• configured their website improperly

How to troubleshoot the error code "SEC_ERROR_UNKNOWN_ISSUER" on secure websites https://support.mozilla.org/en-US/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER

Thanks, I've already been through that.

There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connection certificates and send their own.

https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can

https://support.mozilla.org/en-US/kb/firefox-and-other-browsers-cant-load-websites

https://support.mozilla.org/en-US/kb/secure-connection-failed-error-message

https://support.mozilla.org/en-US/kb/connection-untrusted-error-message

Websites don't load - troubleshoot and fix error messages

http://kb.mozillazine.org/Error_loading_websites

What do the security warning codes mean

Are there other sites where you get the BAD CERT DOMAIN error?

Could you check your connection setting:

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

In the search box at the top of the page, type proxy and Firefox should filter to the "Settings" button, which you can click.

The default of "Use system proxy settings" piggybacks on your Windows/IE "LAN" setting. "Auto-detect" can lead to a flaky connection. You may want to try "No proxy".

Any difference?

Thanks for the suggestion. I don't use proxy. I've seen the problem happen in a few different sites but not all. Mainly i.redd.it .

Thankfully I was able to solve the problem by refreshing Firefox, basically uninstalling it and installing again and losing all settings and addons. Prior to that I tried just disabling all addons and extensions, but that didn't change anything, so they were not the problem.

In short, the solution is uninstalling Firefox.

Hmm, okay, if it comes back, maybe we'll discover why Firefox had a problem with that particular certificate (because it redirects so quickly, it's difficult to see what's going on there).

Correction, the problem is back and not solved. It took a few tries before certificate errors reappeared.

Are they the same errors?

I don't use proxy.

Okay, then changing Firefox's setting to No Proxy should be safe.

Are they the same errors?

Yes, nothing has changed.

needlessOne said

I don't use proxy.

Okay, then changing Firefox's setting to No Proxy should be safe.

I changed the setting to No Proxy. So far nothing has changed.

The thing that's confusing me the most is randomness of the issue. It doesn't consistently happen but when it does all links for the said website are broken.