  Most modern web browsers today sacrifice optimal TLS security for backward
compatibility. They apply coarse-grained TLS configurations that support (by
default) legacy versions of the protocol that have known design weaknesses, and
weak ciphersuites that provide fewer security guarantees (e.g. non Forward
Secrecy), and silently fall back to them if the server selects to. This
introduces various risks including downgrade attacks such as the POODLE attack
[15] that exploits the browsers silent fallback mechanism to downgrade the
protocol version in order to exploit the legacy version flaws. To achieve a
better balance between security and backward compatibility, we propose a
mechanism for fine-grained TLS configurations in web browsers based on the
sensitivity of the domain name in the HTTPS request using a whitelisting
technique. That is, the browser enforces optimal TLS configurations for
connections going to sensitive domains while enforcing default configurations
for the rest of the connections. We demonstrate the feasibility of our proposal
by implementing a proof-of-concept as a Firefox browser extension. We envision
this mechanism as a built-in security feature in web browsers, e.g. a button
similar to the \quotes{Bookmark} button in Firefox browsers and as a
standardised HTTP header, to augment browsers security.
