Christoph Kerschbaumer: Enforcing Security in Firefox

Web browsers were initially designed to retrieve resources on the world wide web in a static manner such that adding security checks in select locations throughout the codebase sufficiently provided the necessary security and privacy guarantees of the web. Instead of opting into security checks wherever resource loads are initiated throughout the codebase, we revamped the security architecture of Firefox so that security checks are performed by default.
This new security enforcement mechanism not only provides the same security guarantees for resource loads which encounter a server-side redirect, but also allows to perform additional privacy checks. For example, Firefox internally extended the Same Origin Policy by an Origin Attributes framework which allows to enforce the First Party Isolation technique for every resource load. First Party Isolation separates browsing contexts by the top-level domain (origin) the user visits to prevent embedded content from tracking users across sites.
Additionally, this new security enforcement mechanism fundamentally enables our HSTS Priming approach, a mechanism which allows to check if a third party HTTP resource is available over HTTPS. Where applicable, this security feature upgrades subresource loads from HTTP to HTTPS.

Christoph Kerschbaumer is a Web Platform Security and Privacy Engineer at Mozilla with over 10 years of experience in Secure Systems Development. His work focuses on all types of content security ranging from providing safe defaults to fighting cross site scripting as well as preventing man-in-the-middle attacks.
He received his PhD in Computer Science from the University of California, Irvine where he based his research on information flow tracking techniques within web browsers.
Prior to being a graduate research scholar, he received a M.Sc. and B.Sc. in Computer Science from the Technical University Graz, Austria.