Mozilla Firefox is also equipped with anti-malware and anti-phishing tools, as well as a download manager, a spellchecker and an RSS Feed Reader. It also comes with enhanced support for HTML5, multi-touch support and an optimized Javascript interpreter named TraceMonkey. Feb 26, 2019  The Core Tools. You can open the Firefox Developer Tools from the menu by selecting Tools Web Developer Toggle Tools or use the keyboard shortcut Ctrl + Shift + I or F12 on Windows and Linux, or Cmd + Opt + I on macOS. The ellipsis menu on the right-hand side of Developer Tools, contains several commands that let you perform actions or change tool settings.

Examine, edit, and debug HTML, CSS, and JavaScript on the desktop and on mobile.

If you are looking for information on using the web developer tools available in Firefox, you've come to the right place — this page provides links to detailed information on all of the core tools and additional tools, and further information such as how to connect to and debug Firefox for Android, how to extend the devtools, and how to debug the browser as a whole.

Please explore the links found in the sidebar, and further down the page. If you have any feedback or questions about the devtools, send us messages on our mailing list or IRC channel (see the community links near the bottom of the page). If you have any feedback or questions specifically about the documentation, the MDN discourse is a good place to post.

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Note: If you are just getting started with web development and using developer tools, our learning web development docs will help you — see Getting started with the Web and What are browser developer tools? for good starting points.

The Core Tools

You can open the Firefox Developer Tools from the menu by selecting Tools > Web Developer > Toggle Tools or use the keyboard shortcut Ctrl + Shift + I or F12 on Windows and Linux, or Cmd + Opt + I on macOS.

The ellipsis menu on the right-hand side of Developer Tools, contains several commands that let you perform actions or change tool settings.

Page Inspector

View and edit page content and layout. Visualise many aspects of the page including the box model, animations, and grid layouts.

Web Console

See messages logged by a web page and interact with the page using JavaScript.

JavaScript Debugger

Stop, step through, examine, and modify the JavaScript running in a page.

Network Monitor

See the network requests made when a page is loaded.

Performance Tools

Analyze your site's general responsiveness, JavaScript, and layout performance.

Responsive Design Mode

See how your website or app will look and behave on different devices and network types.

Accessibility inspector

Provides a means to access the page's accessibility tree, allowing you to check what's missing or otherwise needs attention.

Note: The collective term for the UI inside which the DevTools all live is the Toolbox.

More Tools

These developer tools are also built into Firefox. Unlike the 'Core Tools' above, you might not use them every day.

For the latest developer tools and features, try Firefox Developer Edition.

Connecting the Developer Tools

If you open the developer tools using keyboard shortcuts or the equivalent menu items, they'll target the document hosted by the currently active tab. But you can attach the tools to a variety of other targets, too, both within the current browser and in different browsers or even different devices.

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Debugging the browser

By default, the developer tools are attached to a web page or web app. But you can also connect them to the browser as a whole. This is useful for browser and add-on development.

Extending the devtools

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For information on extending the Firefox DevTools, see Extending the developer tools over in the Browser Extensions section of MDN.

Migrating from Firebug

Firebug has come to the end of its lifespan (see Firebug lives on in Firefox DevTools for details of why), and we appreciate that some people will find migrating to another less familiar set of DevTools to be challenging. To ease a transition from Firebug to the Firefox developer tools, we have written a handy guide — Migrating from Firebug.

Contribute

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If you want to help improve the developer tools, these resources will get you started.

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