Architecture

Introduction to firefox architecture

At a high level, firefox is made of:

• the browser user interface (the main window)
• the web engine, called gecko. Some of its components have been rewritten by using the RUST language.
• the spidermonkey javascript engine
• a set of base components or frameworks: necko, xpcom, etc.

Some components provided by the new servo engine (written in Rust) are:

• webrender, the GPU-based 2D rendering engine
• stylo, the CSS style system

Some major base components or frameworks are:

• xpfe, the mozilla "cross platform Front end" or UI toolkit. It uses XUL, the "XML user interface language", which is interpreted by the browser engine.
• xpcom, the mozilla cross platform component object model
• necko, the network subsystem.
• nss, the Network Security Services
• nspr, the Netscape Portable Runtime. This provides platform independence for non-GUI operating system facilities.

Multiprocess architecture

Multiprocess support was introduced by the Electrolysis project (shortname: e10s). Multiprocess support varies depending on on Firefox versions and platforms. Electrolysis multiprocess support was first introduced in Firefox 48 release.

Process separation insures:

• Stability / Reliability : if a web page or plug in hangs or crashes, the full browser still continues to run.
• Security : Sandboxing (of web pages or plugins) can rely on native process security / access rights mechanisms.

Hence, the following parts of firefox can run in different processes, depending on the target platform:

• browser UI process (1): the top level window and UI.
• web content processes (1..N): They are in charge of one or several tabs (web pages)
• GPU process: for GPU-based compositing
• Legacy NPAPI plugin processes
• Web Extensions processes
• Media playback process
• Service Worker process