Landing into the mainline codebase of Firefox Nightly's mozilla-central repository was vendoring the Servo project, WebRender, the ECMAScript ECMA-262 conformance test suite, and various Rust dependencies.
Servo and WebRender are now landing in the firefox-central code-base, albeit this isn't a magical switchover to using it by default or anything along those lines. Mozilla developers still hope to begin using some Servo components within mainline Firefox by the end of 2017. So a big milestone is crossed but this isn't yet anything that is directly affecting end-users.
The code is now in the Firefox repository and commits to the Servo Git repository now auto-land in the Firefox Mercurial repository automatically. Thus it's becoming easier for Firefox developers to begin making use of Servo, WebRender, and other components in the future as they continue work on Quantum.
Mozilla developer Gregory Szorc wrote on the mailing list A big week for the Firefox repository. He commented, "Altogether, the Firefox repository this week added ~10,000 changesets with ~92,000 file changes across ~37,000 unique files. The number of files in the working directory increased from ~157,000 to ~183,000 with the total file size increasing from ~1,094,000,000 to ~1,158,000,000 bytes (excluding inode size). In my years at Mozilla, I don't recall a single week where we had multiple, independent projects contribute significant changes at this scale. And, we seem to have pulled it all off without melting any servers or inciting mobs of angry developers. Crazy."