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    Other JavaScript tools

    Examine, edit, and debug HTML, CSS, and JavaScript on the desktop and on mobile
    Install Firefox Developer Edition

    What's new in Firefox Developer Edition?

    Firefox Developer Edition is a version of Firefox tailored for developers, featuring the latest Firefox features and experimental developer tools. The current Developer Edition includes these updates to the developer tools:

    Share your ideas

    Share your ideas

    Ask for new features in the developer tools or vote for ideas other developers are asking for.


    Authoring tools for websites and web apps.

    A text editor built into Firefox that lets you write and execute JavaScript.
    Style Editor
    View and edit CSS styles for the current page.
    Shader Editor
    View and edit the vertex and fragment shaders used by WebGL.
    Web Audio Editor
    Examine the graph of audio nodes in an audio context, and modify their parameters.

    Exploring and debugging

    Examine, explore, and debug websites and web apps.

    Web Console
    See messages logged a web page, and interact with the page using JavaScript.
    Page Inspector
    View and modify the page HTML and CSS.
    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.
    Storage Inspector
    Inspect cookies, local storage, indexedDB and session storage present in a page.
    Developer Toolbar
    A command-line interface for the developer tools.
    3D View
    3D visualization of the page.
    Select a color from the page.
    Working with iframes
    How to target a particular iframe.


    Tools for mobile development.

    App Manager
    App Manager has been replaced by WebIDE.
    The replacement for the App Manager, available from Firefox 33 onwards.
    Firefox OS Simulator
    Run and debug your Firefox OS app on the desktop, without needing a real Firefox OS device.
    Responsive Design View
    See how your website or app will look on different screen sizes without changing the size of your browser window.
    Debugging on Firefox for Android
    Connect the developer tools to Firefox for Android.
    Debugging Firefox for Android with WebIDE
    For Desktop Firefox 36+ / Android Firefox 35+, there's a simpler process.
    Connect the developer tools to Chrome on Android and Safari on iOS


    Diagnose and fix performance problems.

    Performance tool
    Analyze your site's general responsiveness, JavaScript and layout performance.
    Frame rate graph
    See the frame rate for your site.
    Figure out what the browser is doing as it runs your site.
    Call Tree
    Figure out where your JavaScript code is spending its time.
    Flame Chart
    See which functions are on the stack over the course of a performance profile.
    Paint Flashing Tool
    Highlights the parts of the page that are repainted in response to events.
    Reflow Event Logging
    See reflow events in the web console.
    Network Performance
    See how long the parts of your site take to load.



    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.

    Browser Console
    See messages logged by the browser itself and add-ons, and run JavaScript code in the browser's scope.
    Browser Toolbox
    Attach the Developer Tools to the browser itself.

    Extending the devtools

    The developer tools are designed to be extensible. Firefox add-ons can access the developer tools and the components they use to extend existing tools and add new tools. With the remote debugging protocol you can implement your own debugging clients and servers, enabling you to debug websites using your own tools or to debug different targets using the Firefox tools.

    Add a new panel to the devtools
    Write an add-on that adds a new panel to the Toolbox.
    Remote Debugging Protocol
    The protocol used to connect the Firefox Developer Tools to a debugging target like an instance of Firefox or a Firefox OS device.
    Source Editor
    A code editor built into Firefox that can be embedded in your add-on.
    The Debugger Interface
    An API that lets JavaScript code observe the execution of other JavaScript code. The Firefox Developer Tools use this API to implement the JavaScript debugger.
    Web Console custom output
    How to extend and customize the output of the Web Console and the Browser Console.
    Example devtools add-ons
    Use these examples to understand how to implement a devtools add-on.

    More resources

    This section lists resources which aren't maintained by Mozilla's developer tools team, but which are widely used by web developers. We've included a few Firefox add-ons in this list, but for the complete list see the “Web Development” category on

    A very popular and powerful web development tool, including a JavaScript debugger, HTML and CSS viewer and editor, and network monitor.
    DOM Inspector
    Inspect, browse, and edit the DOM of web pages or XUL windows.
    Web Developer
    Adds a menu and a toolbar to the browser with various web developer tools.
    Webmaker Tools
    A set of tools developed by Mozilla, aimed at people getting started with Web development.
    W3C Validators
    The W3C website hosts a number of tools to check the validity of your website, including its HTML and CSS.
    JavaScript code analysis tool.

    Join the Developer tools community

    Choose your preferred method for joining the discussion:

    Document Tags and Contributors

    Contributors to this page: Sheppy
    Last updated by: Sheppy,