directory_structure.md

firefox-main/docs/contributing/directory_structure.md

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# Firefox Source Code Directory Structure

This article provides an overview of what the various directories contain.

To simply take a look at the Firefox source code, you do not need to

download it. You can look at the source directly with your web browser

using Searchfox (start at <https://searchfox.org/firefox-main/source> for

the complete firefox source code of branch HEAD).

In order to modify the source, you have to acquire it either by

downloading a {ref}`snapshot <Firefox Contributors' Quick Reference>` of the sources or

by checking out the current sources from

{ref}`the repository <Firefox Contributors' Quick Reference>`.

This document describes the directory structure -- i.e., directories that

are used by at least some of the

Mozilla project's client products. There are other directories in the

other Mozilla repository, such as those for Web tools and those for the

Classic codebase.

See the [more detailed overview of the pieces of Gecko](https://wiki.mozilla.org/Gecko:Overview).

## .cargo

Configuration files for the [Cargo package

manager](https://crates.io/).

## .vscode

Configuration files used by the [Visual Studio Code

IDE](https://code.visualstudio.com/) when working in the

mozilla-central tree.

## accessible

Files for accessibility (i.e., MSAA (Microsoft Active Accessibility),

ATK (Accessibility Toolkit, used by GTK) support files). See

[Accessibility](https://developer.mozilla.org/docs/Web/Accessibility).

## browser

Contains the front end code (in XUL, Javascript, XBL, and C++) for the

Firefox desktop browser. Many of these files started off as a copy of files in

[xpfe](#xpfe).

## browser/extensions

Contains [PDF.js](https://mozilla.github.io/pdf.js/) and

[WebCompat](https://github.com/mozilla/webcompat-addon) built-in extensions.

## browser/themes

Contains images and CSS files to skin the browser for each OS (Linux,

Mac and Windows)

## build

Miscellaneous files used by the build process. See also [config](#config).

## caps

Capability-based web page security management. It contains C++ interfaces

and code for determining the capabilities of content based on the

security settings or certificates (e.g., VeriSign). See [Component

Security](https://www.mozilla.org/projects/security/components/) .

## chrome

{ref}`Chrome registry <Chrome Registration>` used with [toolkit](#toolkit)/.

These files were originally copies of files in `rdf/chrome/`.

## config

More files used by the build process, common includes for the makefiles,

etc.

## devtools

The Firefox Developer Tools server and client components. See {ref}`contributor <devtools-contributor-doc>` and {ref}`user <devtools-user-doc>` documentation.

## docs

Contains the documentation configuration ([Sphinx](http://www.sphinx-doc.org/) based), the index page

and the contribution pages.

## docshell

Implementation of the 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.

## dom

- {ref}`IDL definitions <XPIDL>` of the interfaces defined by

  the DOM specifications and Mozilla extensions to those interfaces

  (implementations of these interfaces are primarily, but not

  completely, in content).

- The parts of the connection between JavaScript and the

  implementations of DOM objects that are specific both to JavaScript

  and to the DOM.

- Implementations of a few of the core "DOM Level 0" objects, such as

  [window](https://developer.mozilla.org/docs/Web/API/Window) , [window.navigator](https://developer.mozilla.org/docs/Web/API/Window/navigator), [window.location](https://developer.mozilla.org/docs/Web/API/Window/location), etc.

## editor

The editor directory contains XUL/Javascript for the embeddable editor

component, which is used for the HTML Editor("Composer"), for plain and

HTML mail composition, and for text fields and text areas throughout the

product. The editor is designed like a

"browser window with editing features": it adds some special classes for

editing text and managing transaction undo/redo, but reuses browser code

for nearly everything else.

## extensions

Contains several extensions to mozilla, which can be enabled at

compile-time using the `--enable-extensions` configure argument.

Note that some of these are now built specially and not using the

`--enable-extensions` option. For example, disabling xmlextras is done

using `--disable-xmlextras`.

## extensions/auth

Implementation of the negotiate auth method for HTTP and other

protocols. Has code for SSPI, GSSAPI, etc. See [Integrated

Authentication](https://www.mozilla.org/projects/netlib/integrated-auth.html).

## extensions/pref

Preference-related extensions.

## extensions/spellcheck

Spellchecker for mailnews and composer.

## extensions/universalchardet

Detects the character encoding of text.

## gfx

Contains interfaces that abstract the capabilities of platform specific

graphics toolkits, along with implementations on various platforms.

These interfaces provide methods for things like drawing images, text,

and basic shapes. It also contains basic data structures such as points

and rectangles used here and in other parts of Mozilla.

## gradle

Containing files related to a Java build system.

## hal

Contains platform specified functions (e.g. obtaining battery status,

sensor information, memory information, Android

alarms/vibrate/notifications/orientation, etc)

## image

Image rendering library. Contains decoders for the image formats Firefox

supports.

## intl

Internationalization and localization support. See

[L10n:NewProjects](https://wiki.mozilla.org/L10n:NewProjects).

## intl/locale

Code related to determination of locale information from the operating

environment.

## intl/lwbrk

Code related to line breaking and word breaking.

## intl/strres

Code related to string resources used for localization.

## intl/uconv

Code that converts (both ways: encoders and decoders) between UTF-16 and

many other character encodings.

## intl/unicharutil

Code related to implementation of various algorithms for Unicode text,

such as case conversion.

## ipc

Container for implementations of IPC (Inter-Process Communication).

## js/src

The JavaScript engine, also known as

{ref}`SpiderMonkey <SpiderMonkey>`.

See also [JavaScript](https://developer.mozilla.org/docs/JavaScript).

## js/xpconnect

Support code for calling JavaScript code from C++ code and C++ code from

JavaScript code, using XPCOM interfaces. See

[XPConnect](https://developer.mozilla.org/docs/XPConnect).

## layout

Code that implements a tree of rendering objects that describe the types

and locations of the objects that are displayed on the screen (such as

CSS boxes, tables, form controls, XUL boxes, etc.), and code that

manages operations over that rendering tree (such as creating and

destroying it, doing layout, painting, and event handling). See

[documentation](https://www.mozilla.org/newlayout/doc/) and [other

information](https://www.mozilla.org/newlayout/).

## layout/base

Code that deals with the rendering tree.

## layout/forms

Rendering tree objects for HTML form controls.

## layout/generic

The basic rendering object interface and the rendering tree objects for

basic CSS boxes.

## layout/mathml

Rendering tree objects for [MathML](https://developer.mozilla.org/docs/Web/MathML).

## layout/svg

Rendering tree objects for [SVG](https://developer.mozilla.org/docs/Web/SVG).

## layout/tables

Rendering tree objects for CSS/HTML tables.

## layout/xul

Additional rendering object interfaces for [XUL](https://developer.mozilla.org/docs/XUL) and

the rendering tree objects for XUL boxes.

## media

Contains sources of used media libraries for example *libpng*.

## memory

Cross-platform wrappers for *memallocs* functions etc.

## mfbt

Implementations of classes like *WeakPtr*. Multi-platform *assertions*

etc.

## mobile

## mobile/android

Firefox for Android and Geckoview

## modules

Compression/Archiving, math library, font (and font compression),

Preferences Library

## modules/libjar

Code to read zip files, used for reading the .jar files that contain the

files for the mozilla frontend.

## modules/libpref

Library for reading and writing preferences.

## modules/zlib

Source code of zlib, used at least in the networking library for

compressed transfers.

## mozglue

Glue library containing various low-level functionality, including a

dynamic linker for Android, a DLL block list for Windows, etc.

## netwerk

{ref}`Networking library <Networking>`, also known as Necko.

Responsible for doing actual transfers from and to servers, as well as

for URI handling and related stuff.

## netwerk/cookie

Permissions backend for cookies, images, etc., as well as the user

interface to these permissions and other cookie features.

## nsprpub

Netscape Portable Runtime. Used as an abstraction layer to things like

threads, file I/O, and socket I/O. See {ref}`NSPR`.

## nsprpub/lib

Mostly unused; might be used on Mac?

## other-licenses

Contains libraries that are not covered by the MPL but are used in some

Firefox code.

## parser

Group of structures and functions needed to parse files based on

XML/HTML.

## parser/expat

Copy of the expat source code, which is the XML parser used by mozilla.

## parser/html

The HTML parser (for everything except <about:blank>).

## parser/htmlparser

The legacy HTML parser that's still used for <about:blank>. Parts of it

are also used for managing the conversion of the network bytestream into

Unicode in the XML parsing case.

## parser/xml

The code for integrating expat (from parser/expat) into Gecko.

## python

Cross module python code.

## python/mach

The code for the {ref}`Mach` building tool.

## security

Contains NSS and PSM, to support cryptographic functions in mozilla

(like S/MIME, SSL, etc). See {ref}`Network Security Services (NSS)`

and

[Personal Security Manager

(PSM)](https://www.mozilla.org/projects/security/pki/psm/).

## services

Firefox accounts and sync (history, preferences, tabs, bookmarks,

telemetry, startup time, which addons are installed, etc). See

[here](https://docs.services.mozilla.com/).

## servo

[Servo](https://servo.org/), the parallel browser engine project.

## startupcache

XXX this needs a description.

## storage

[Storage](https://developer.mozilla.org/docs/Mozilla/Tech/XPCOM/Storage): XPCOM wrapper for sqlite. Wants to

unify storage of all profile-related data. Supersedes mork. See also

[Unified Storage](https://wiki.mozilla.org/Mozilla2:Unified_Storage).

## taskcluster

Scripts and code to automatically build and test Mozilla trees for the

continuous integration and release process.

## testing

Common testing tools for mozilla codebase projects, test suite

definitions for automated test runs, tests that don't fit anywhere else,

and other fun stuff.

## third_party

Vendored dependencies maintained outside of Mozilla.

## toolkit

The "new toolkit" used by Thunderbird, Firefox, etc. This contains

numerous front-end components shared between applications as well as

most of the XBL-implemented parts of the XUL language (most of which was

originally forked from versions in `xpfe/`).

## toolkit/mozapps/extensions/test/xpinstall

The installer, which contains code for installing Mozilla and for

installing XPIs/extensions. This directory also contains code needed to

build installer packages. See [XPInstall](https://developer.mozilla.org/docs/XPInstall) and

the [XPInstall project

page](https://www.mozilla.org/projects/xpinstall/).

## tools

Some tools which are optionally built during the mozilla build process.

## tools/lint

The linter declarations and configurations.

See [linting documentation](/code-quality/lint/)

## uriloader

## uriloader/base

Content dispatch in Mozilla. Used to load uris and find an appropriate

content listener for the data. Also manages web progress notifications.

See [Document Loading: From Load Start to Finding a

Handler](https://www.mozilla.org/docs/docshell/uri-load-start.html)

and [The Life Of An HTML HTTP

Request](https://www.mozilla.org/docs/url_load.html).

## uriloader/exthandler

Used to handle content that Mozilla can't handle itself. Responsible for

showing the helper app dialog, and generally for finding information

about helper applications.

## uriloader/prefetch

Service to prefetch documents in order to have them cached for faster

loading.

## view

View manager. Contains cross-platform code used for painting, scrolling,

event handling, z-ordering, and opacity. Soon to become obsolete,

gradually.

## widget

A cross-platform API, with implementations on each platform, for dealing

with operating system/environment widgets, i.e., code related to

creation and handling of windows, popups, and other native widgets and

to converting the system's messages related to painting and events into

the messages used by other parts of Mozilla (e.g., `view/` and

`content/`, the latter of which converts many of the

messages to yet another API, the DOM event API).

## xpcom

[Cross-Platform Component Object Model](/en-US/docs/XPCOM). Also

contains data structures used by the rest of the mozilla code. See also

[XPCOM Project](https://www.mozilla.org/projects/xpcom/).

## xpfe

XPFE (Cross Platform Front End) is the SeaMonkey frontend. It contains

the XUL files for the browser interface, common files used by the other

parts of the mozilla suite, and the XBL files for the parts of the XUL

language that are implemented in XBL. Much of this code has been copied

to `browser/` and `toolkit/` for use in

Firefox, Thunderbird, etc.

## xpfe/components

Components used by the Mozilla frontend, as well as implementations of

interfaces that other parts of mozilla expect.