Firefox services: Services like logging, remote settings, firefox account...
Gecko: Mozilla web rendering engine (See also the new Servo engine). Gecko's function is to read web content, such as HTML, CSS, XUL, JavaScript, and render it on the user's screen or print it. In XUL-based applications Gecko is used to render the application's user interface as well.
Mozilla Cross Platform Component Object Model: XPCOM is a cross platform component object model, similar to Microsoft COM. It has multiple language bindings, allowing XPCOM components to be used and implemented in JavaScript, Java, and Python in addition to C++. Interfaces in XPCOM are defined in a dialect of IDL called XPIDL.
Mozilla Cross Platform Connect: XPConnect enables simple interoperation between XPCOM and JavaScript (Scriptable Components)
Necko: Necko is a network library that provides a platform-independent API for several layers of networking, ranging from transport to presentation layers. This API is used in many Mozilla-based client applications (including Firefox) and can be used for writing other networking clients.
Servo: Servo is an experimental browser engine written in RUST. It takes advantage of memory safety properties and concurrency features of the Rust programming language.
Docshell: The main object managing things related to a document window. Each frame has its own docshell. It contains methods for loading URIs, managing URI content listeners, etc. It is the outermost layer of the embedding API used to embed a Gecko browser into an application.
GeckoServo: GeckoServo imports Servo web engine components into the Gecko web engine, replacing some gecko legacy components.
GeckoView: GeckoView is an Android library project that allows third-party developers to use Gecko as an Android View in their own applications.
Libxul: Provides a static build of "gecko" including XPCOM, networking, DOM, layout, rendering, and embedding modules in one shared library (avoids exposing many shared libraries)
Network Security Services (NSS): NSS is a set of libraries designed to support cross-platform development of security-enabled applications.
Servo Webrender: WebRender is a GPU-based 2D rendering engine written in Rust. Firefox, the research web browser Servo, and other GUI frameworks draw with it.
techno
Mach: Mach is a build-tool used to build mozilla apps
Marionette: Marionette is a remote protocol that lets out-of-process programs communicate with, instrument, and control Gecko-based browsers.
WebExtensions: The WebExtensions API is a cross-browser system for developing extensions.
XML User Interface Language: XUL is Mozilla's XML-based language for building user interfaces of applications like Firefox.
developer
Firefox Developer Tools: Firefox Developer Tools is a set of web developer tools built into Firefox. You can use them to examine, edit, and debug HTML, CSS, and JavaScript.
Firefox Remote Protocol: Low-level debugging interface. This can be used to inspect the state and control execution of documents running in web content, instrument Gecko, simulate user interaction for automation purposes, and debug JavaScript execution.
Rust-bindgen: rust-bindgen is a C++ bindings generator for the Rust language.
project
ETP: Enhanced Tracking Protection includes multiple privacy features, including tracking cookie restrictions and a new Storage Access API.
Oxidation: Oxidation is a project to integrate Rust code in and around Firefox.
Quantum: Quantum is Mozilla's project to build the next-generation web engine for Firefox users, building on the Gecko engine as a solid foundation. Quantum will leverage the fearless concurrency of Rust and high-performance components of Servo to bring more parallelization and GPU offloading to Firefox.
QuantumCompositor: Quantum Compositor moves Gecko’s compositor into its own process. Moving code that interacts with the GPU into its own process will make Firefox more stable.
QuantumDOM: The Quantum DOM project will make Gecko more responsive, especially when there are a lot of background tabs open. Goals: Classify and prioritize tasks on the main thread; Preempt tasks that are running the background tabs if this preempting is not noticeable to the user.
QuantumFlow: Browser responsiveness improvement effort focused on User centric performance and responsiveness (prioritized over throughput).
Stylo (a.k.a. Quantum CSS): Integrates Servo's CSS style system into Gecko, such that the style system code can be shared by Gecko and Servo.
closed project
Electrolysis: The Electrolysis project implements Multiprocess support in Firefox (shortname: e10s). This project is now complete.
MemShrink: Firefox project to reduce memory consumption (2011-2014)