In addition to most browser makers focusing on the everyday user looking to surf the Web, they also cater to the Web developers, designers and quality assurance professionals who help build the apps and sites that those users are accessing by integrating powerful tools right into the browsers themselves. Firefox's Web Developer section includes tools for designers, developers, and testers alike such as a style editor and pixel-targeting eyedropper. Recently the Firefox team has lead the Dev Tools pack with tools for Grid, Flexbox, and more.

1. Click on Firefox's main menu button, represented by three horizontal lines and located in the upper right-hand corner of the browser window.
   
2. When the drop-down menu appears, select the icon labeled Developer. The Web Developer menu should now be displayed, containing the following options. You'll notice that most menu items have keyboard shortcuts associated with them.

   
   Toggle Tools: Displays or hides the developer tools interface, typically positioned at the bottom of the browser window. Keyboard shortcut: Mac OS X (ALT(OPTION)+COMMAND+I), Windows (CTRL+SHIFT+I)

   
   Inspector: Allows you to inspect and/or tweak CSS and HTML code on the active page as well as on a portable device via remote debugging. Keyboard shortcut: Mac OS X (ALT(OPTION)+COMMAND+C), Windows (CTRL+SHIFT+C)

   
   Web Console: Allows you to execute JavaScript expressions within the active page as well as review a diverse set of logged data including security warnings, network requests, CSS messages, and more. Keyboard shortcut: Mac OS X (ALT(OPTION)+COMMAND+K), Windows (CTRL+SHIFT+K)

   
   Debugger: The JavaScript Debugger lets you pinpoint and fix defects by setting breakpoints, inspecting DOM nodes, black boxing external sources, and much more. As is the case with the Inspector, this feature also supports remote debugging. Keyboard shortcut: Mac OS X (ALT(OPTION)+COMMAND+S), Windows (CTRL+SHIFT+S)

   
   Style Editor: Allows you to create new stylesheets and incorporate them with the active Web page, or edit existing sheets and test how your changes render in a browser with just one click. Keyboard shortcut: Mac OS X, Windows (SHIFT+F7)
   
   
Performance: Provides a detailed breakdown of the active page's network performance, frame rate data, JavaScript execution time and state, paint flashing, and much more. Keyboard shortcut: Mac OS X, Windows (SHIFT+F5)

   
   Network: Lists each network request initiated by the browser along with the corresponding method, origin domain, type, size, and time elapsed. Keyboard shortcut: Mac OS X (ALT(OPTION)+COMMAND+Q), Windows (CTRL+SHIFT+Q)

   
   Developer Toolbar: Opens an interactive command line interpreter. Enter help into the interpreter for a list of all available commands and their proper syntax. Keyboard shortcut: Mac OS X, Windows (SHIFT+F2)
WebIDE: Provides the ability to create and execute Web apps through an actual device running Firefox OS or via the Firefox OS Simulator. Keyboard shortcut: Mac OS X, Windows (SHIFT+F8)

   
   Browser Console: Provides the same functionality as the Web Console (see above). However, all data returned is for the entire Firefox application (including extensions and browser-level functions) as opposed to just the active Web page. Keyboard shortcut: Mac OS X (SHIFT+COMMAND+J), Windows (CTRL+SHIFT+J)
   
   
Responsive Design View: Allows you to instantly view a Web page in different resolutions, layouts, and screen sizes to mimic multiple devices including tablets and smartphones. Keyboard shortcut: Mac OS X (ALT(OPTION)+COMMAND+M), Windows (CTRL+SHIFT+M)

   
   Eyedropper: Displays the hex color code for individually selected pixels.
Scratchpad: Lets you write, edit, integrate and execute snippets of JavaScript code from within a pop-out Firefox window. Keyboard shortcut: Mac OS X, Windows (SHIFT+F4)
   
   
Page Source: The original browser-based developer tool, this option simply displays the available source code for the active page. Keyboard shortcut: Mac OS X (COMMAND+U), Windows (CTRL+U)

   
   Get More Tools: Opens the Web Developer's Toolbox collection on Mozilla's official add-ons site, featuring about a dozen popular extensions such as Firebug and Greasemonkey.