Multiprocess Firefox

In older versions of desktop Firefox, the entire browser was running in a single operating system process. In particular, the JavaScript that ran the browser UI (also known as "chrome code") used to run in the same process as the code in web pages (also known as "content" or "web content").

Latest versions of Firefox run the browser UI in a separate process from web content. In the first iteration of this architecture, all browser tabs run in the same process and the browser UI runs in a different process. In future iterations, we expect to have more than one content process. The project that's delivering multiprocess Firefox is called Electrolysis, sometimes abbreviated to e10s.

Normal web pages are unaffected by multiprocess Firefox. People working on Firefox itself and Firefox add-on developers will be affected if their code relies on being able to access web content directly.

Instead of accessing content directly, chrome JavaScript will have to use the message manager to access content. To help ease the transition we've implemented Cross Process Object Wrappers and some compatibility shims for add-on developers. If you are an add-on developer wondering whether you are affected, see the guide to working with multiprocess Firefox.

Technical overview
A very high-level view of how multiprocess Firefox is implemented.
Web content compatibility guide
Guidelines and details on potential Web site compatibility issues that may arise due to the transition. Tip: there aren't very many!
A reference for the jargon used in multiprocess Firefox.
Message manager
Complete guide to the objects used to communicate between chrome and content.
SDK-based add-ons
How to migrate add-ons developed using the Add-on SDK.
Which URIs load where
A quick guide to which URIs - chrome:, about:, file:, resource: - are loaded into which process.
Why we are implementing multiprocess Firefox: performance, security, and stability.
Add-on migration guide
If you are an add-on developer, find out if you are affected and how to update your code.
Cross Process Object Wrappers
Cross Process Object Wrappers are a migration aid, giving chrome code synchronous access to content.
Debugging content processes
How to debug code running in the content process, including frame and process scripts.
Tab selection in multiprocess Firefox
How switching tabs works in multiprocess Firefox.

Limitations of chrome scripts
Practices that will no longer work in chrome code, and how to fix them.
Limitations of frame scripts
Practices that will not work inside frame scripts, and what to do instead.

Contact us

Find out more about the project, get involved, or ask us your questions.

Document Tags and Contributors

 Last updated by: fscholz,