Using 0-RTT data reduces the latency of requests using TLS, and the latency overhead needed to deploy TLS. With Fizz TLS 1.3's speed is on par with Zero protocol, so Facebook has replaced Zero ...

Mitigating BEAST involved upgrading to TLS 1.1 or 1.2, the latest versions of the TLS protocol, or prioritizing unaffected RC4-based cipher suites for older versions of the protocol.