Firefox Developer Tools

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  • Revision title: Firefox Developer Tools
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The Firefox Developer Tools enable you to analyze and debug websites and web apps on Firefox Desktop, Firefox OS, and Firefox for Android.

You can use them to examine and edit HTML and CSS, to debug JavaScript, and to run JavaScript in the page. You can use them to see network requests that your browser makes as well as any JavaScript and CSS warnings and errors that it encounters when loading a page. You can use them to debug performance problems with your site.

The tools aren't just for debugging on desktop Firefox. They're built using a client-server protocol that enables a tool running on the desktop to debug code running on an Android device running Firefox, and will soon enable you to debug code running on Firefox OS as well.

We've also provided some tools that specifically target mobile development: the Responsive Design View is a quick way to see how a site will look on a small screen, and the Firefox OS Simulator lets you run and debug a Firefox OS app on the desktop without needing to use a real Firefox OS device.

Finally, the developer tools are extensible by design. Firefox add-ons can access the debugger API, so you can build your own developer tools that extend and enhance the built-in 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.

 What's new in Aurora?

The current Aurora release is Firefox 25, and includes these new features:

  • block box libraries in the JavaScript debugger

  • edit and replay network requests

  • CSS autocompletion in the Inspector

  • import and export profile data

Toolbox

The Toolbox provides a single home for most of the developer tools that are built into Firefox.
 
Page Inspector
View and modify the HTML and CSS for the selected element.
Web Console
See informational, warning and error messages emitted by the browser loading a web page, and examine and manipulate the page using JavaScript.
Style Editor
View and edit CSS styles for the current page.
JavaScript Debugger
Step through JavaScript code that is running in the browser and watch variables to help track down bugs.
JavaScript Profiler
Use the profiler to figure out where your JavaScript code is spending its time.
Network Monitor
Inspect all the network requests that are made when a page is loaded, and how long they take to execute.

Mobile

Of course, mobile web developers are web developers too, so the web development tools listed above are mostly interesting to mobile web developer as well. But we've also created some tools specifically aimed at mobile development.

 
Remote Debugging
Use the developer tools to debug your Android device over USB.
Firefox OS Simulator
Run and debug your Firefox OS app on the desktop, without needing to use 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.

These tools ship inside Firefox as well, but their user interfaces aren't integrated into the Toolbox.

Scratchpad
A text editor built into Firefox that lets you write and execute JavaScript.
Browser Console
See messages from all JavaScript code running in the browser including content, chrome, and add-ons. Execute JavaScript code in the chrome window's context.
Developer Toolbar
A command-line interface to manipulate and work with the developer tools in Firefox, and buttons for quick access to the most commonly used tools.
3D View
Also known as "Tilt", this provides a 3D visualisation of the current page.
Paint Flashing Tool
The paint flashing tool highlights the part of the browser window that are repainted in response to events, helping to diagnose potential performance problems with your site.
 

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 addons.mozilla.org.

 
Firebug
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.
JSHint
JavaScript code analysis tool.

Getting help

If you have any questions about the developer tools built into Firefox, please come and ask us on the dev-developer-tools mailing list or in the #devtools channel on Mozilla's IRC network. You can also find out more about the team on our Wiki page.

Revision Source

<p>The Firefox Developer Tools enable you to analyze and debug websites and web apps on <a href="http://www.mozilla.org/en-US/firefox/fx/#desktop" title="http://www.mozilla.org/en-US/firefox/fx/#desktop">Firefox Desktop</a>, <a href="http://www.mozilla.org/en-US/firefox/os/" title="http://www.mozilla.org/en-US/firefox/os/">Firefox OS</a>, and <a href="http://www.mozilla.org/en-US/firefox/fx/#mobile" title="http://www.mozilla.org/en-US/firefox/fx/#mobile">Firefox for Android</a>.</p>
<p><img alt="" src="https://mdn.mozillademos.org/files/6041/firefox-developer-tools.png" style="width: 800px; height: 584px;" />You can use them to <a href="/en-US/docs/Tools/Page_Inspector" title="/en-US/docs/Tools/Page_Inspector">examine and edit HTML and CSS</a>, to <a href="/en-US/docs/Tools/Debugger" title="/en-US/docs/Tools/Debugger">debug JavaScript</a>, and to <a href="/en-US/docs/Tools/Web_Console#The_command_line_interpreter" title="/en-US/docs/Tools/Web_Console#The_command_line_interpreter">run JavaScript in the page</a>. You can use them to <a href="/en-US/docs/Tools/Network_Monitor" title="/en-US/docs/Tools/Network_Monitor">see network requests</a> that your browser makes as well as any <a href="/en-US/docs/Tools/Web_Console" title="/en-US/docs/Tools/Web_Console">JavaScript and CSS warnings and errors</a> that it encounters when loading a page. You can use them to <a href="/en-US/docs/Tools/Profiler" title="/en-US/docs/Tools/Profiler">debug performance problems with your site</a>.<br />
  <br />
  The tools aren't just for debugging on desktop Firefox. They're built using a <a href="https://wiki.mozilla.org/Remote_Debugging_Protocol" title="https://wiki.mozilla.org/Remote_Debugging_Protocol">client-server protocol</a> that enables a tool running on the desktop to <a href="/en-US/docs/Tools/Remote_Debugging" title="/en-US/docs/Tools/Remote_Debugging">debug code running on an Android device running Firefox</a>, and will soon enable you to debug code running on Firefox OS as well.<br />
  <br />
  We've also provided some tools that specifically target mobile development: the <a href="/en-US/docs/Tools/Responsive_Design_View" title="/en-US/docs/Tools/Responsive_Design_View">Responsive Design View</a> is a quick way to see how a site will look on a small screen, and the <a href="/en-US/docs/Tools/Firefox_OS_Simulator" title="/en-US/docs/https://developer.mozilla.org/en-US/docs/Tools/Firefox_OS_Simulator">Firefox OS Simulator</a> lets you run and debug a Firefox OS app on the desktop without needing to use a real Firefox OS device.</p>
<p>Finally, the developer tools are extensible by design. Firefox add-ons can access the debugger API, so you can build your own developer tools that extend and enhance the built-in tools. With the <a href="https://wiki.mozilla.org/Remote_Debugging_Protocol" title="https://wiki.mozilla.org/Remote_Debugging_Protocol">remote debugging protocol</a> 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.</p>
<div class="geckoVersionNote">
  <h3 id=".C2.A0What's_new_in_Aurora.3F"><a href="https://hacks.mozilla.org/2013/08/new-features-of-firefox-developer-tools-episode-25/" title="https://hacks.mozilla.org/2013/08/new-features-of-firefox-developer-tools-episode-25/">&nbsp;What's new in Aurora?</a></h3>
  <p>The <a href="http://www.mozilla.org/en-US/firefox/aurora/" title="http://www.mozilla.org/en-US/firefox/aurora/">current Aurora release</a> is Firefox 25, and includes these new features:</p>
  <ul>
    <li>
      <p><a href="/en-US/docs/Tools/Debugger#Black_box_a_source" title="/en-US/docs/Tools/Debugger#Black_box_a_source">block box libraries</a> in the JavaScript debugger</p>
    </li>
    <li>
      <p>edit and replay network requests</p>
    </li>
    <li>
      <p>CSS autocompletion in the Inspector</p>
    </li>
    <li>
      <p>import and export profile data</p>
    </li>
  </ul>
</div>
<div class="cleared topicpage-table">
  <div class="section">
    <h2 class="Tools" id="Tools" name="Tools">Toolbox</h2>
    The <a href="/en-US/docs/Tools/Toolbox" title="/en-US/docs/Tools/Toolbox">Toolbox</a> provides a single home for most of the developer tools that are built into Firefox.<br />
    <dl>
      <dt>
        &nbsp;</dt>
      <dt>
        <a href="/en-US/docs/Tools/Page_Inspector" title="Tools/Page_Inspector">Page Inspector</a></dt>
      <dd>
        View and modify the HTML and CSS for the selected element.</dd>
      <dt>
        <a href="/en-US/docs/Tools/Web_Console" title="Tools/Web_Console">Web Console </a></dt>
      <dd>
        See informational, warning and error messages emitted by the browser loading a web page, and examine and manipulate the page using JavaScript.</dd>
      <dt>
        <a href="/en-US/docs/Tools/Style_Editor" title="Tools/Style_Editor">Style Editor</a></dt>
      <dd>
        View and edit CSS styles for the current page.</dd>
      <dt>
        <a href="/en-US/docs/Tools/Debugger" title="Tools/Debugger">JavaScript Debugger</a></dt>
      <dd>
        Step through JavaScript code that is running in the browser and watch variables to help track down bugs.</dd>
      <dt>
        <a href="/en-US/docs/Tools/Profiler" title="Tools/Profiler">JavaScript Profiler</a></dt>
      <dd>
        Use the profiler to figure out where your JavaScript code is spending its time.</dd>
      <dt>
        <a href="/en-US/docs/Tools/Network_Monitor" title="Tools/Network_Monitor">Network Monitor</a></dt>
      <dd>
        Inspect all the network requests that are made when a page is loaded, and how long they take to execute.</dd>
    </dl>
    <h2 class="Community" id="Community" name="Community">Mobile</h2>
    <p>Of course, mobile web developers are web developers too, so the web development tools listed above are mostly interesting to mobile web developer as well. But we've also created some tools specifically aimed at mobile development.</p>
    <dl>
      <dt>
        &nbsp;</dt>
      <dt>
        <a href="/en-US/docs/Tools/Remote_Debugging" title="Tools/Remote_Debugging">Remote Debugging</a></dt>
      <dd>
        Use the developer tools to debug your Android device over USB.</dd>
      <dt>
        <a href="/en-US/docs/Tools/Firefox_OS_Simulator" title="Tools/Firefox_OS_Simulator">Firefox OS Simulator</a></dt>
      <dd>
        Run and debug your Firefox OS app on the desktop, without needing to use a real Firefox OS device.</dd>
      <dt>
        <a href="/en-us/docs/Tools/Responsive_Design_View" title="/en-us/docs/Tools/Responsive_Design_View">Responsive Design View</a></dt>
      <dd>
        See how your website or app will look on different screen sizes without changing the size of your browser window.</dd>
    </dl>
  </div>
  <div class="section">
    <h2 class="Related_Topics" id="Related_Topics" name="Related_Topics">Standalone Tools</h2>
    <p>These tools ship inside Firefox as well, but their user interfaces aren't integrated into the Toolbox.</p>
    <dl>
      <dt>
        <a href="/en-US/docs/Tools/Scratchpad" title="Tools/Scratchpad">Scratchpad</a></dt>
      <dd>
        A text editor built into Firefox that lets you write and execute JavaScript.</dd>
      <dt>
        <a href="/en-us/docs/Tools/Browser_Console" title="/en-us/docs/Tools/Responsive_Design_View">Browser Console</a></dt>
      <dd>
        See messages from all JavaScript code running in the browser including content, chrome, and add-ons. Execute JavaScript code in the chrome window's context.</dd>
      <dt>
        <a href="https://developer.mozilla.org/en-US/docs/Tools/GCLI" title="en/Tools/GCLI">Developer Toolbar</a></dt>
      <dd>
        A command-line interface to manipulate and work with the developer tools in Firefox, and buttons for quick access to the most commonly used tools.</dd>
      <dt>
        <a href="/en-US/docs/Tools/3D_View" title="Tools/3D_View">3D View</a></dt>
      <dd>
        Also known as "Tilt", this provides a 3D visualisation of the current page.</dd>
      <dt>
        <a href="/en-US/docs/Tools/Paint_Flashing_Tool" title="Tools/Paint_Flashing_Tool">Paint Flashing Tool</a></dt>
      <dd>
        The paint flashing tool highlights the part of the browser window that are repainted in response to events, helping to diagnose potential performance problems with your site.</dd>
      <dt>
        &nbsp;</dt>
    </dl>
    <h2 class="Documentation" id="Documentation" name="Documentation">More Resources</h2>
    <p>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 <a href="https://addons.mozilla.org/en-US/firefox/extensions/web-development/" title="https://addons.mozilla.org/en-US/firefox/extensions/web-development/">"Web Development" category on addons.mozilla.org</a>.</p>
    <dl>
      <dt>
        &nbsp;</dt>
      <dt>
        <a href="https://www.getfirebug.com/" title="Firebug">Firebug</a></dt>
      <dd>
        A very popular and powerful web development tool, including a JavaScript debugger, HTML and CSS viewer and editor, and network monitor.</dd>
      <dt>
        <a href="https://developer.mozilla.org/en-US/docs/DOM_Inspector" title="DOM_Inspector">DOM Inspector</a></dt>
      <dd>
        Inspect, browse, and edit the DOM of web pages or XUL windows.</dd>
      <dt>
        <a href="https://addons.mozilla.org/en-US/firefox/addon/web-developer/" title="Web-Developer">Web Developer</a></dt>
      <dd>
        Adds a menu and a toolbar to the browser with various web developer tools.</dd>
      <dt>
        <a href="https://webmaker.org/en-US/tools/" title="https://webmaker.org/en-US/tools/">Webmaker Tools</a></dt>
      <dd>
        A set of tools developed by Mozilla, aimed at people getting started with Web development.</dd>
      <dt>
        <a href="http://www.w3.org/Status.html" title="W3C">W3C Validators</a></dt>
      <dd>
        The W3C website hosts a number of tools to check the validity of your website, including its <a href="http://validator.w3.org/" title="http://validator.w3.org/">HTML</a> and <a href="http://jigsaw.w3.org/css-validator/" title="http://jigsaw.w3.org/css-validator/">CSS</a>.</dd>
      <dt>
        <a href="http://www.jshint.com/" title="JSHint">JSHint</a></dt>
      <dd>
        JavaScript code analysis tool.</dd>
    </dl>
  </div>
</div>
<h2 id="Getting_help">Getting help</h2>
<p>If you have any questions about the developer tools built into Firefox, please come and ask us on the <a href="https://lists.mozilla.org/listinfo/dev-developer-tools" title="https://lists.mozilla.org/listinfo/dev-developer-tools">dev-developer-tools</a> mailing list or in the <a href="http://mibbit.com/?channel=%23devtools&amp;server=irc.mozilla.org">#devtools</a> channel on <a href="http://irc.mozilla.org/">Mozilla's IRC network</a>. You can also find out more about the team on our <a href="https://wiki.mozilla.org/DevTools" title="https://wiki.mozilla.org/DevTools">Wiki page</a>.</p>
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