Who is this?

Need some technical help.  Firefox is now popping up these security screens on me frequently.  I would appreciate some advice about who this is and why it's intruding all of a sudden.  Comment or email, whichever is easier for you.  Here are two screenshots (click to enlarge). 

Comments

[Bob]

I encounter this infrequently. I just close it. I figure it's a bug
or I have to adjust cookies.

Not a big irritant for me.

[Fat Man]

I just ignore them, but I do not know what they mean. If you find out. Please tell us.

[Owyn]

This is merely windows giving you a heads up that a persons certificate not being from a liscensed certificate authority((a black hole to put your money)). The primary use for such a certificate is to provide users with a way of identifying your website((Or target website)) as legitiment.

We have a certificate at my company that we didn't buy from one of the authorities but it still identifies our site as our site because it was issued to us by us so we know that it is a proper Certificate, you are safe as long as you are going to kovidgoyal's website, A poetry site I believe

[Owyn]

My fault a physics student at CalTech

[db48x]

It means that you visited a secure site (https://kovidgoyal.net/ in this case), but the certificate that the site is using to encrypt and sign the connection could not be verified. It's a self-signed certificate, which is sufficient for encryption purposes but not to verify identity.

Of course, the fact that all of that information is basically present in the first dialog only indicates that people don't really read the dialogs that their computer presents them. Of course it's not really your fault you didn't read it - you only see it when you're trying to accomplish some task, which means that it's always an interruption that you would like to dismiss as quickly as possible.

[Andrew]

Like db48x said, it means the certificate is not signed by an authority. Each browser comes loaded with a default set of authorities that the browser knows it can trust (Verisign, Thawte, etc). When you go to an encrypted website, it gives your browser it's certificate as a form of id. The certificate has the url of the site and the issuer of the certificate. If the url doesn't match, you get that error. If the issuer is not known as an authority, the browser attempts to check that site's certificate as well. Eventually the browser will work it's way up the chain to an authority it trusts, or it will give you that error if it can't. Of course, it caches all this as it goes, so after a while it has a pretty good tree of authority built up that it can reference as trusted.

The pop up basically means: "Your data to this site is encrypted, but I can't guarantee that the person you are sending it to is who they say they are."

It's just too bad the popup doesn't put it in plain english, because while it's safe to ignore on a site you aren't spending money at, I wouldn't give my credit card to a self-signed site.