This is correct. Servo's Stylo parallelized CSS parser shipped in Firefox's "Quantum" performance release, but a huge part of the overall performance improvemen

This is correct. Servo's Stylo parallelized CSS parser shipped in Firefox's "Quantum" performance release, but a huge part of the overall performance improvement came from profiling the whole system. Fixing lots of small hot spots in Firefox frontend and Gecko really added up. It's easy for tiny performance regressions to creep in here and there.