for Gecko. Quantum Quantum is a Mozilla project encompassing several software development efforts to "build the next-generation web engine for Firefox users". It includes numerous improvements to Gecko, largely incorporated from the experimental Servo project. Quantum also includes refinements to the user interface and interactions. Firefox 57, released in November 2017, is the initial version with a Servo component enabled. Mozilla dubs this and several planned future releases "Firefox Quantum". Background In 2012, Mozilla began the experimental Servo project, which is an engine designed from scratch with the goals of improving concurrency and parallelism while also reducing memory safety vulnerabilities. Servo is written in the Rust programming language, also created by Mozilla, which is designed to generate compiled code with better memory safety, concurrency, and parallelism than compiled C++ code. As of April 2016, Servo needed at least several years of development to become a full-featured browser engine, hence the decision to start the Quantum project to bring stable portions of Servo into Firefox. Mozilla laid off all Servo developers in August 2020. Components The Quantum project is composed of several sub-projects. CSS: Servo's parallel style sheet system integrated into Gecko. Benchmarks suggest that performance scales linearly with number of CPU cores. This was released in Firefox 57. Render: Servo's rendering architecture, called WebRender, integrated into Gecko. WebRender replaces the immediate mode drawing model with a retained mode model that is more easily accelerated by the GPU by taking advantage of CSS/DOM's similarity to a scene graph. Worst-case scenario rendering in testing exceeds 60 frames per second. Mozilla began enabling the new renderer for select hardware/OS combinations in Firefox 67. Compositor: Gecko's existing compositor moved to its own process, isolating browser tabs from graphics driver related crashes. Since compositor crashes will not bring down the browser content process, the compositor process can be restarted transparently without losing user data. This was released in Firefox 53. DOM: Loosely inspired by Servo's Constellation architecture and Opera's Presto engine, Quantum DOM uses cooperatively scheduled threads within the DOM to increase responsiveness without increasing the number of processes and, thus, memory usage. The core of this shipped in Firefox 57. Flow: An umbrella for user visible performance improvements driven by a team that works across Gecko components. Focused on real user performance improvements on major webapps, primarily G Suite (now called Google Workspace) and Facebook. This work completed and shipped for Firefox 57. Photon: