Slightly simplified: Each and every CA that's trusted by your browser is capable of issuing a certificate for every single domain on the internet. A certificate

Slightly simplified: Each and every CA that's trusted by your browser is capable of issuing a certificate for every single domain on the internet. A certificate is basically nothing more than a document saying "StartSSL has verified that the certificate you're seeing right now belongs to the owner of google.com", with some crypto sprinkled on top. The only thing that's preventing you from getting a certificate for any domain are software checks implemented on their end. If one of these checks fail (i.e. because the methodology is broken, or there's a bug, or they can be bypassed), you can get a certificate for any domain.