Developer Edition 48 – Firebug features, editable storage, inspector improvements and more…

This week marks the release of Firefox Developer Edition 48. In preparation for the arrival of multiprocess Firefox and the deprecation of the Firebug add-on, we are porting Firebug features to the built-in tools. We have also made tweaks to the current tools that we’ll cover in this post.

Firebug theme

As part of porting Firebug features to the built-in tools, we’re also porting the Firebug theme, giving Firebug users a more familiar environment to work with. This is the initial release of the theme so please let us know if you find any bugs and report them here. Here is a screenshot of the Firebug theme:

Firebug theme

DOM panel

The DOM panel is another feature we are porting from Firebug. This panel provides a handy tree view which allows you to browse and inspect the DOM structure of your page. Here’s a screenshot of the new tool:

DOM Panel screenshot

Editable storage

Editing support inside the storage inspector is one of the most frequently requested features. In this release, we added the ability to edit and delete cookies, local storage, and session storage entries. You can edit a cell by double-clicking on it. You can also delete entries by using the context menu.
Editable storage entries

Deletable cells

Geometry editor

In this release, we have added a new visual editing tool that allows you to easily tweak the positioning of any absolutely positioned or fixed-position element. You can change the values of the top, left, bottom and right properties using this tool. To launch the geometry editor, go to the Box Model tab in the inspector and click on the Geometry editor icon icon.

Geometry Editor

Memory tool improvements

The memory tool is now enhanced with a brand new tree-map view that gives a quick and intuitive visual overview of how memory is being used. This new view groups objects together by their types, which allows you to easily see the quantity of similar items (arrays when drawing canvas lines, scripts when loading a script-heavy website, etc.) taking up memory. Also, the size of each item in the map is proportional to the amount of bytes used, which allows you to easily see which items are taking up most of your memory.

Memory tool tree map

The memory tool provides a useful aggregate view that groups all instances of the same type of node. In this release, you can now click the ? icon to view all individual instances of a specified type in a separate view. You can also view the retaining paths of those individual nodes, using the retaining paths panel added in the previous release. This allows you to precisely pinpoint how a specific object is leaking when debugging your web app.

Aggregate view individual nodes

Finally, we have also added the ability to remove individual snapshots from the memory tool sidebar.

Inspector improvements

We have polished the user experience in the inspector to make it smoother and easier to use. The Rules view autocomplete now selects the most used property by default to make your authoring experience faster. For example, background will be selected instead of backface-visibility because it’s more frequently used. Here is a screencast of the feature in action:

Better rules view autocomplete

We have also improved the way long values are handled in the Rules view. A new multi-line mode specifically for long values lets you conveniently reach and select different parts of the value you’re editing.

Multi-line mode

The markup view now emphasises the relationship between a parent node and its children. The selected element now has a line underneath it that highlights the child nodes. This allows you to easily spot the selected element child nodes when the HTML markup is complex.

Parent child relationship

A quick way to switch between different angle units in the Rules view has been added. There is now a swatch next to angle values which you can shift-click to cycle between different units, similar to the colour values interaction. This feature was added by contributor Nicolas Chevobbe.

Cycle between angle units

Finally, we have added keyboard shortcuts to easily navigate between the markup view search results. You can now use Shift+Enter to navigate backwards within the search results. Also, Ctrl/Cmd+G and Ctrl/Cmd+Shift+G now work as aliases for Enter and Shift+Enter. These keyboard shortcuts were added by contributor Steve Melia.

Console improvements

The console has also received various tweaks that will make your daily experience with the tool more enjoyable. The first improvement comes from the set of Firebug features we’re porting. You can now expand network logs to inspect them and reveal a Firebug-style details view. Here is a screenshot:

Inline HTTP inspection

If you’re working with Map or Set objects, you can now view and inspect their individual entries from the console sidebar. This feature was added by contributor Jarda Snajdr.

Improved Map/Set inspection

Finally, we have added support for console.clear() to clear the console output.

about:debugging features

In preparation for the release of WebExtensions, we’ve added a feature that will be a great help to add-on developers. You can now reload add-ons from about:debugging, which allows you to quickly develop your add-on without having to re-install it every time you make a change.

Reloading add-ons with about:debugging

If you’re working with Service Workers, you’ll notice that we have added a way to unregister individual workers. Here is a screenshot:

Unregister service workers

Other notable changes

In addition to the changes above, we have polished various areas of the toolbox including:

Thanks to everyone who contributed to this release! Make sure to grab a fresh copy of Firefox Developer Edition and share your thoughts! If you have feedback about different Firebug features being ported, we’d love to hear your suggestions and constructive comments here.

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Toolbox, Inspector & Scratchpad improvements – Firefox Developer Tools Episode 32

Firefox 32 was just uplifted to the Aurora release channel, so let’s take a look at the most important Developer Tools changes in this release.

First, we would like to thank all 41 people who contributed patches to DevTools this release! Here is a list of all DevTools bugs resolved for Firefox 32.


We’ll start out the list with a couple of features that were requested on the new UserVoice feedback channel that we are trying out.

Node dimensions are now displayed in the box model infobar. Similar to how other tools work, you can easily refer to the dimensions of the highlighted node directly from the infobar. (development notes & UserVoice request)

Screenshot of node dimensions being shown in the infobar above the box model highlighter

The ‘pick an element from the page’ button is now closer to the inspector tab so it is quicker to jump between them. Protip: you can also use the Ctrl+Shift+C or Cmd+Opt+C keyboard shortcuts to do the same thing. (development notes & UserVoice request)

Screenshot of the new Inspect Element position on the left side of the toolbox

There is now a ‘full page screenshot’ command button. After enabling this button, just press it and a screenshot will appear in your downloads folder. (development notes)

Screenshot of taking a screenshot of the current page with DevTools

A demonstration of the screenshot can be seen in the animated gif below:

Animated gif of taking a screenshot of the current page with DevTools

New images are being used throughout the DevTools UI to support high pixel density displays (HiDPI), so the UI looks much sharper on these devices. Big thanks to our contributor Tim Nguyen for his hard work on these changes! (development notes)

Web Audio Editor

Joining the Shader Editor and Canvas Debugger, the Web Audio Editor is a new media tool that has landed in Firefox 32. After enabling it in the options panel, you can inspect the AudioContext graph and modify properties on AudioNodes. Stay tuned for another Hacks post very soon with more details.

Screenshot of the new web audio tool


User agent styles can be shown in the Inspector. Since these default styles can interact with your page styles, it is handy to see them. This can be enabled from the options panel, and there is more documentation about this feature on MDN. (development notes & UserVoice request)

Screenshot of viewing user agent styles in the Inspector Panel

Animated gif of viewing user agent styles in the Inspector Panel

Hidden nodes are now displayed differently from visible nodes in the markup view. (development notes & UserVoice request)

Screenshot of hidden nodes being displayed differently in the Inspector panel

Web fonts are previewable within the font inspector tooltip. When hovering a font stack, you will see the currently applied font in the tooltip (including any web fonts). (development notes)

Screenshot of a web font being previewed in the Inspector panel

There is now a ‘Paste Outer HTML’ context menu entry for nodes in the markup view. (development notes & UserVoice request)


There is now type-inference based code completion for JavaScript in Scratchpad. Open a list of suggestions at your current cursor position with Ctrl+Space and type information about the current symbol can be shown with Shift+Space. It is being powered by the excellent tern code-analysis engine. (development notes)

Screenshot of scratchpad showing an autocompletion list

Screenshot of scratchpad showing type information about a function

Do you have feedback, bug reports, feature requests, or questions? As always, you can comment here, add/vote for ideas on UserVoice or get in touch with the team at @FirefoxDevTools on Twitter.

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asm.js performance improvements in the latest version of Firefox make games fly!

The latest version of Firefox which launched last week includes a major update to the user interface as well as to features like Sync. Another area in which this release brings significant improvements is in asm.js performance, which as we will see below is very important for things like games. To put that aspect of Firefox’s performance in context, we’ll take a look at benchmark results comparing Firefox to other browsers, which show that Firefox is faster at executing asm.js code.

asm.js speedups

asm.js is a subset of JavaScript that is very easy to optimize and is particularly useful for porting code in C or C++ to the Web. We’ve blogged about how Firefox can optimize asm.js code using 32-bit floating point operations, which, together with all the other work on optimizing asm.js, allows it to run at around 1.5x slower than the speed of the same C/C++ when compiled natively. So, while not quite native speed yet, things are getting very close. At the time of that blog post those optimizations were only on nightly builds, but they are now reaching hundreds of millions of Firefox users in Firefox 29, which is now the release version of Firefox.

Another important set of asm.js optimizations concern startup speed. As blogged about by Luke a few months ago, Firefox performs ahead of time (AOT) compilation and can cache the results, for significant speedups in startup times. Those optimizations also shipped to users in Firefox 29.

Web browser comparisons

Now that all those optimizations have shipped, it’s interesting to look at up-to-date browser comparisons on asm.js code. The above graph shows the Emscripten benchmark suite running the latest stable versions of Google Chrome, Internet Explorer and Firefox on Windows 8.1. Lower numbers are better in all the results here, which are real-world codebases compiled to asm.js (see notes in the graph).

Unity, Emscripten and asm.js

asm.js is a subset of JavaScript, so it is just one of many styles of JavaScript out there. But it represents an important use case. As we announced at GDC, Unity, one of the most popular game creation tools on the market, will support the Web by using Emscripten to compile their engine to asm.js.

But videos are no substitute for the real thing! You can try the games shown there in your browser right now, for instance with Unity’s recently released Angry Bots demo. If you run those in the latest version of Firefox, you’ll see many of the asm.js optimizations mentioned earlier in action. For example, if you visit one of those links more than once then asm.js caching will allow it to avoid recompiling the game (so it starts up faster), and also gameplay will be smoother due to faster asm.js execution.

Being able to execute asm.js-style code efficiently makes it possible for games like this to run well on the Web, without proprietary, nonstandard plugins. That’s why it’s exciting to see more asm.js optimizations reach Firefox users in Firefox 29. And while benchmark results can sometimes seem like nothing more than abstract numbers, speedups on asm.js benchmarks directly improve things like games, where performance is extremely important and very noticeable.

(Thanks to Marc Schifer for helping with the benchmark measurements.)

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Box model highlighter, Web Console improvements, Firefox OS HUD + more – Firefox Developer Tools Episode 30

Firefox 30 was just uplifted to the Aurora release channel, so let’s take a look at the most important DevTools changes in this release.


One of our most requested features has been to highlight box model regions of elements on the page. We are happy to report that this feature has landed in Firefox 30. One of the great things is that the colors of the box model highlighter match the box model diagram found in the right pane of the inspector more clearly than before.

Check out the inspector documentation to read more about the new functionality, or just see the screenshot and short video below:

Inspector box model highlighter

There is a new font family tooltip to the CSS rule view. Hover over a font-family value to see an inline preview of the font. (development notes)

Inspector font family preview

Web Console

There are some big improvements in the web console to help view and navigate output.

Sample console output

Highlight and jump to nodes from console

Running the cd() command in the console switches the scope between iframes. Read more in the cd command documentation. (development notes)

Console cd() command

You can read more from Mihai about the ongoing changes to the web console. He has also been documenting the web console API for extension authors.

Firefox OS

The network monitor is now working with Firefox OS. (development notes)

There is now memory tracking (development notes) and jank tracking (development notes) in the Firefox OS Developer HUD. You can read much more about jank (aka “event loop lag”) in Paul’s Firefox OS: tracking reflows and event loop lags.

Firefox OS Developer HUD

Network Monitor

The Network Monitor has a new look to go along with some new features:

  • The design of the network timeline has been updated, which has actually improved scroll performance on the panel. (development notes)
  • Hovering over a request with an image response now shows a popup with the image. (development notes)
  • Network requests with an image response now display a thumbnail near the file name. (development notes)

Network Monitor Timeline UI

Network requests with a JSON-like response will show an object preview, even if the response type is plain text. (development notes)

JSON Response in Network Monitor


There is new behavior for console shortcut key (cmd+alt+k or ctrl+shift+k). It now focuses the input line in web console at all times, opening the toolbox if necessary but never closing it. There are more details about this change on robcee’s blog. (development notes)

To save some space on the top toolbar, there are now options to hide command buttons, like Scratchpad. The only buttons enabled by default now are Inspect Element, Split Console, and Responsive Mode. More information about this change on the devtools mailing list. (development notes). To enable Scratchpad, Paint Flashing, or Tilt, just click on the checkbox in the options panel.

Enabling Command Buttons on Toolbar

We would like to give a special thanks to all 46 people who contributed patches to DevTools this release! Here is a list of all DevTools bugs resolved for Firefox 30.

Do you have feedback, bug reports, feature requests, or questions? As always, you can comment here or get in touch with the team at @FirefoxDevTools.

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HTML Editing and other improvements in Firefox 17 Developer Tools

Firefox 17 has recently hit the Aurora channel, and with it comes a number of  improvements to the built-in web developer tools.

HTML Editing

This is one of the most-requested features for our tools, and we’re happy with the solution we have for you. With the Style panel in the Page Inspector, you can easily manipulate the styles on the page. When you’re working on a layout, however, you sometimes need to manipulate the DOM of the page as well. The new “Markup panel” lets you do just that.

The new Markup Panel

To open the Markup panel, open the Page Inspector and click on the button that looks like an outline and appears right next to the “breadcrumbs” in the toolbar. In the screenshot above, that button is the third from the left. You can also press ctrl-M to open the Markup Panel.

As before, you can choose elements to inspect in the Style panel by clicking on them in the Markup panel. You can also right-click on the elements in the Markup panel to access a couple of handy features (copy HTML, delete the node).

What’s new in this version of the Markup panel? Previously, you could double click on an attribute value to change that value. Now you can double click almost anywhere to change anything. Double click on text to change the text. Likewise for the tag itself. See that space just before the closing “>” of a tag? Double click there and you can add new attributes.

You’ll also find that keyboard navigation for getting around and editing the DOM is easy to work with. You can use the tab key to move around within a tag and the arrow keys to move between nodes.

Note: the screenshot above shows the Markup panel with a dark theme. The plan is to replace this with a light theme before the feature is released.

More to love in the Web Console

The Web Console remains a favorite tool among web developers, and we’re happy to have even more improvements for you in this release.

Updated Web Console theme

The most visible change in the Web Console is the refreshed toolbar. The Web Console now has an appearance in line with the rest of the Firefox developer tools.

The screenshot above also shows off another improvement: better autocompletion. We’ve found and fixed some cases (like string objects) where the Web Console wasn’t giving as much help as it could.

Another important change to note: the Web Console comes with a helper function called $. Previously, that function was an alias for document.getElementById. In conjunction with other browser consoles, we’re changing it to be document.querySelector which is far more useful. To get the behavior you had before, just add a # at the beginning of the argument you pass in (for example, $("#myElementID")). You can continue to use $$ as an alias for document.querySelectorAll. If you’re using jQuery, the $ helper function will be replaced by jQuery, so this change won’t affect you.

Want to be able to see the Web Console’s text a bit more clearly? You can now zoom the Web Console using the same controls you use to zoom the browser window (ctrl-+, ctrl– and ctrl-0 to reset on Windows/Linux. Use cmd-+, cmd– and cmd-0 on Mac).

Using the built-in console.log function is a very handy way to add tracing to your web application. Now, if you send an object to console.log, you can now click on that object in the output area of the Web Console in order to inspect it.

Also in the screenshot above, you’ll see the “More Tools” button in the Developer Toolbar at the bottom of the window. That button gives you quick access to the rest of the developer tools. (Sharp-eyed readers might notice a mysterious “JSTerm” button on my Developer Toolbar. That’s Paul Rouget’s JSTerm add-on, which is really nice to use. Check it out!)

Page Inspector Visual Update

We’ve been listening to feedback from web designers since the Page Inspector made its debut on the Aurora channel last November. We found that the appearance of the dark “veil” over everything but the selected element was striking, but also making it harder for designers to see styling changes they made in the context of their overall design. We added options to turn off the page dimming a few months ago, but in this update we’ve got a lighter approach:

Updated highlighting in the Page Inspector

Instead of darkening the whole page, we highlight the selected element using a subtle dashed line and the useful node toolbar. Even better, when you move your cursor to the Style panel to try out style changes, the highlighting fades away entirely so that you can focus entirely on the styling.

Debugger Improvements

The Latest Debugger

The Debugger has had tons of improvements, some visible and some not, since it hit Aurora three months ago. One of the visible changes that you can see in the screenshot above: search across all scripts! Just go to the find box and start your search with “!” (exclamation point) and you’ll rapidly find matches across all of the scripts in the area just below the toolbar.

If you want more space to look at your code, there’s a new button in the toolbar (the second button on the left in the screenshot) that will close the two side panels to give your code all of the room it needs.

Finally, we’ve got more keyboard shortcuts to make using the Debugger quicker than ever:

  • alt-shift-P (Windows), ctrl-shift-P (Mac) to focus the search box
  • alt-shift-T (Windows), ctrl-shift-T (Mac) to do a string (token) search
  • F6 for continue
  • F7 for step over
  • F8 for step in
  • shift-F8 for step out

Update: One more debugger improvement to call out: as noted in the Firefox 15 release notes, there was a problem with the debugger not hitting its breakpoints on page reload. This is fixed in Firefox 16 (which is now in Beta).

Try Aurora: it’s good for you!

All of these changes are available today on the Aurora channel and are scheduled for release later in the year. I think you’ll find that Aurora works quite well, so give it a try and let us know what you think via the Feedback button!

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Firefox Aurora 13 is out – SPDY on by default and a list of other improvements

We have just released Aurora 13, together with a number of improvements.


There are a couple of things we’d like to shine some extra light on here:

SPDY on by default

The SPDY control brings responsive and scalable transport to Firefox. It allows for multiplexing and connection sharing and is SSL only. It will offer faster page loads and better scalability for SPDY-enabled web servers.

Our first implementation was in Firefox 11, but now with Firefox Aurora 13 it is on by default!

User Agent change for Mobile

The preferred way for web sites to offer content depending on the device is to use CSS Media Queries. However, there is a good amount of user agent sniffing still going on out there, so we wanted to make you aware of the change/difference between Firefox on mobile phones and on tablets, as outlined in Mobile and Tablet indicators.

For Firefox on mobile it will be:

Mozilla/5.0 (Android; Mobile; rv:13.0) Gecko/13.0 Firefox/13.0

Firefox on tablets will be:

Mozilla/5.0 (Android; Tablet; rv:13.0) Gecko/13.0 Firefox/13.0

List of improvements

Here are all the improvements we’ve made complete with links to each bug listing for those who want to read up more on respective implementation.






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Aurora 12 is out – improvements and updated Developer Tools

Aurora 12 is out, together with updated Developer Tools, and these are the improvements/changes.


A few of the improvements that stand out a little more:

ECMAScript Harmony’s Simple Map and Set builtins

For testing purposes, we have implemented ECMAScript Harmony’s Simple Map and Set builtins. This is only in Aurora and will be disabled when it goes to beta, so plase test it out now and give feedback! There is also MDN documentation on Set and MDN documentation on Map if you want to learn more.

If you are more interested in Harmony progress, read up on our implementation work for ECMAScript 6

Support multitouch on Android

We’re happy to now have implemented multitouch for Firefox on Android!

Let authors put line breaks (newlines) in tooltips (title attribute)

It might seem like a small thing, but have been discussed quite some time. You can now use newlines for tooltips!

XMLHttpRequest should allow to specify a network timeout in ms (for async requests)

Instead of timeouts and similar, this offers a way to speficy a network timeout for XMLHttpRequests using the timeout attribute.

List of improvements

Here are all the improvements we’ve made complete with links to each bug listing for those who want to read up more on respective implementation.







Developer Tools

There has been a total of 89 improvements to Web Console, Scratchpad, Style Editor, Page Inspector, Style Inspector, HTML view and Page Inspector 3D view (Tilt). Here are the highlights:

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WEB EXCLUSIVE: Improvements coming to the port of Davisville

By LINDSAY OLIVIER 12-Monday.jpg NORTH KINGSTOWN – Last year, Quonset was the recipient of $22.3 million worth of federal Transportation Investment Generating Economic Recovery (TIGER) grants for major improvements to the Port of Davisville. The improvements have begun and continue to run on schedule. By the time the improvements are completed …

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Oracle aims to boost client-side Java with JavaFX improvements

At the Oracle OpenWorld event, the database giant revealed some details about its Java roadmap. Oracle unsurprisingly wants to continue improving Java Enterprise Edition, but the company also highlighted its commitment to improving client-side Web support and mobile application development with JavaFX. The Java programming language plays an important role in facilitating third-party mobile …

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