It is? Same FAQ page you listed: "When you download an application file, Firefox will verify the signature. If it is signed, Firefox then compares the signatur

It is? Same FAQ page you listed: "When you download an application file, Firefox will verify the signature. If it is signed, Firefox then compares the signature with a list of known safe publishers. For files that are not identified by the lists as “safe” (allowed) or as “malware” (blocked), Firefox asks Google’s Safe Browsing service if the software is safe by sending it some of the download’s metadata."