Developer Tools in Firefox Aurora 10

The Preview You Can Use Now

Mozilla is building a collection of stable, fast and usable developer tools that ship with the browser. I’d like to introduce a collection of improvements that are scheduled to be released in final form on January 31, 2012.

But, you can get them now by downloading the Firefox Aurora channel. I personally find Aurora builds to be quite stable and usable for general browsing and web development. Give it a try and see what you think. You can install Aurora alongside your stable release of Firefox.

The New Page Inspector

Inspect Element Context Menu

Using built-in tools, you can now peek into your page’s structure and layout. Choose “Inspect” from the “Web Developer” menu, or press the handy ctrl-shift-I (cmd-shift-I on Mac) keyboard shortcut, and you can visually select the page element that is of interest to you.

You’ll also find a new “Inspect Element” context menu item that lets you immediately select the element that’s under your cursor.

When you’re inspecting a page, you’ll see something like this:

We overlay the page to highlight the element that you’re working with (1). The highlighter also shows you the tag, ID and classes associated with the page element you’re viewing.

At the bottom of the window, there’s a toolbar that gives you options for changing or working with the selected element. Starting from the left, there’s a close button to close the page inspector and return to normal browsing. The “Inspect” button toggles visual selection mode so that you can highlight another element. ProTip: pressing the ESC key also switches modes.

We call the next part of the toolbar the “breadcrumbs”. They show you where you are in the HTML structure and let you quickly switch to another element. The selected element is the dark “pushed” button. To the left of it are its parents, and to the right one of its children. Just click one of the buttons to move between the page elements. If you click and hold a button, you get a menu that lets you select from the siblings of the element listed on the button. The breadcrumbs make navigation quick without taking up much of your screen.


Sometimes looking at the HTML representation of a page is the quickest way to figure out what’s going on. Click the HTML button and that’s the view you’ll get. There’s a resizer on the right side of the toolbar to set just how much space you want for the HTML view. Also, clicking on a node in the HTML view will select that element for further inspection. ProTip: ctrl-H toggles the HTML view.


Last, but definitely not least, is the Style view. This lets you dive in, explore and experiment with your CSS. It offers two separate views of the CSS attached to the selected element: a CSS rules-based view (left, above), and a properties-based view (right, above).

The rules view is organized much like your stylesheets, showing all of the rules that apply to the element and all of those properties that those rules give you. Properties that are overridden are crossed out. You can toggle any single property easily using the checkbox to the left of it. A single click on a property name or value lets you edit it and see the results immediately on the page. If you click anywhere on the line with the brace at the bottom of the rule, you can add a new property there.

On a page with lots of styles, you sometimes just want to find out what the font-size is set to. That’s where the property view comes in. You can expand the “font-size” property and see how its set and which stylesheet set it. By default, only styles that are set in your stylesheets will be displayed (so you don’t get browser defaults listed). If you have a lot of properties listed, as you might if you use a reset stylesheet, you can quickly find what you’re looking for by typing in the search box.

ctrl-S toggles the Style view.

Web Console + Page Inspector: Great Together

The Web Console is available whenever you want it, even when you’re using the page inspector. If you have an element selected, that element is available to JavaScript in the console using the variable $0.


The Scratchpad feature, which we released in August, gives you a very friendly way to experiment with JavaScript. Rather than being confined to a small input box, you get a whole editor window to work with. Now, Scratchpad uses the Orion code editor to provide syntax highlighting, better indentation and other features you’d expect from a modern code editor.

Scratchpad is now wired into Firefox’s “session restore” feature. This means that you can try out a bunch of code in Scratchpad and if you restart Firefox, restoring your session will also bring back your Scratchpad. Of course, you can always save and reload your Scratchpad files, just as you could before.

If you are only doing web development, we’ve streamlined the user interface. If you’re doing Firefox add-on development, you owe it to yourself to set to true in about:config. That setting allows Scratchpad to run code in a privileged browser context and not just against the current web page.

The console Object

We’ve been building out the console object that you call from your JavaScript code or use at the Web Console’s JavaScript input. It is now in line with the de facto standard, implementing the methods that are standard across browsers. Firebug has a couple of others that we don’t implement yet (console.table, console.profile, console.dirxml), but the commonly used methods are there.

More Is On The Way

All of these features are available now in Firefox Aurora builds. We’re working on getting more new features together for you for the next Aurora.

Check out our Get Involved page to see how you can provide feedback and help make these tools even better.


1. Other web developer tools make changes to your page (for example, adding a class) to make the selected element visible. Firefox’s highlighter does its work without making any changes to your content .↩


  1. suraj

    This is a great tool for web developers. Thanks Mozilla team

    July 11th, 2012 at 04:31

  2. markk morann

    this is an EXCELENT TOOL for dev.
    I have active this tool, but in my laptop: Fujitsu N6200 series…
    i got a problem..I can see 3D buttom…why?
    is a video card problem?
    I have only [style] buttom

    How to resolve this problem? …
    in another computer no problem…

    October 6th, 2012 at 00:37

    1. Kevin Dangoor

      Take a look at the video card blocklist:

      October 6th, 2012 at 08:01

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