hello, this preference is only there for a transitional period in firefox 31 and 32. in later versions only the pkix certificate authentification system will be used.

Screen in the attachment.

Thanks for the tempestive answer, Philipp.

Then, what do I've to do?

Because, the sotry is as the following: since the afternoon I'm not able to access anymore the PLESK's control panel of one of the website I made. Every time I try Aurora gives me the message "(Error code: sec_error_ca_cert_invalid)". After confirming the situation, I immediately contacted the support service of the provider in charge of my hosting, telling them the whole thing. After 30 minutes, they suggested me to follow the instrunctions at this link: http://blog.dob.sk/2014/07/23/firefox-31-self-signed-certificate-sec_error_ca_cert_invalid/ writing that the last update of Firefox was the fault.

Basically, that's how I ended here.

then i think the best avenue to continue is using the release version of firefox 31 at the moment) available at https://www.mozilla.org/firefox/channel/#firefox and filing a bug report about your issue so that it can be resolved properly...

You can contact the website and point them to this article as they need to fix this security vulnerability on their side:

See "Behavior Changes" and "Things for CAs to Fix":

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

That is one of the reasons that you should always have the current release installed if you use Firefox development versions.

• http://kb.mozillazine.org/Testing_pre-release_versions