Firefox 3.5 for developers

Firefox 3.5 (released June 30, 2009) introduces a number of new features, as well as additional and improved support for a wide variety of web standards. This article offers an extensive list, with links to articles covering the major improvements.

New developer features in Firefox 3.5

For website and application developers

HTML 5 support

Using audio and video

Firefox 3.5 adds support for the HTML 5 audio and video elements.

Offline resources in Firefox

Firefox 3.5 now fully supports the HTML 5 offline resource specification.

Drag and drop

The HTML 5 drag and drop API allows support for dragging and dropping items within and between websites. This also provides a simpler API for use by extensions and Mozilla-based applications.

Newly-supported CSS features

Downloadable fonts support

The new @font-face @rule lets web pages provide downloadable fonts, so that sites can be rendered exactly as the page author expects.

CSS media queries

Firefox 3.5 now supports CSS media queries, which enhance support for media-dependent style sheets.

::before and ::after updated to CSS 2.1

The ::before and ::after pseudo-elements have been updated to full CSS 2.1 support, adding support for the position, float, list-style-*, and some display properties.

ch units for length

The ch unit can now be used anywhere that accepts a unit of length. 1ch is the width of the "0" (zero) character.


The -moz-opacity Mozilla extension to CSS has been removed in favor of the standard opacity property.


The text-shadow property, which allows web content to specify shadow effects to apply to text and text decorations, is now supported.


This newly-supported property lets content specify whether or not lines may be broken within words in order to prevent overflow when an otherwise unbreakable string is too long to fit on one line.

white-space property supports the pre-line value

The white-space property now accepts the pre-line value.







Firefox 3.5 adds support for these Mozilla extensions to CSS.

The -moz-nativehyperlinktext color value

This new color value represents the user's system's default hyperlink color.

The -moz-window-shadow property and the :-moz-system-metric(mac-graphite-theme) pseudo-class

These new CSS features were added to facilitate theming.

New values for -moz-appearance

The -moz-win-glass and -moz-mac-unified-toolbar values have been added to -moz-appearance.

Using CSS transforms

Firefox 3.5 supports CSS transforms. See -moz-transform and -moz-transform-origin for details.


These selectors are all newly-supported in Firefox 3.5.

New DOM features


Firefox 3.5 adds support for the Web Storage localStorage property, which provides a way for web applications to store data locally on the client's computer.

Using web workers

Firefox 3.5 supports web workers to allow easy multi-threading support in web applications.

Using geolocation

Firefox 3.5 supports the Geolocation API, which allows web applications to obtain information about the user's current location if a provider for that information is installed and enabled.

Locating DOM elements using selectors

The selectors API allows querying a document to locate the elements that match a given selection rule.

Mouse gesture events

Firefox 3.5 supports mouse gesture events such as trackpad swipes.

The NodeIterator object

The NodeIterator object provides support for iterating over the list of the nodes in a DOM subtree.

The MozAfterPaint event

This new DOM event is sent after painting updates in windows.

The MozMousePixelScroll event

This new DOM event allows detection of pixel-based mouse scroll wheel events instead of line-based scroll events.

New JavaScript features

New in JavaScript 1.8.1

An overview of all the changes in JavaScript 1.8.1.


This new method returns the prototype of a specified object.

Using native JSON

Firefox 3.5 has native support for JSON.

New trim methods on the String object

The String object now has trim(), trimLeft(), and trimRight() methods.


Cross-site access controls for HTTP

In Firefox 3.5, it's now possible for HTTP requests, including those made by XMLHttpRequest, to work across domains if the server supports it.

Progress events for XMLHttpRequest

Progress events are now offered to enable extensions to monitor the progress of requests.

Improved Synchronous XMLHttpRequest support

DOM Timeout and Input Events are now suppressed during a synchronous XMLHttpRequest.

Controlling DNS prefetching

Firefox 3.5 provides DNS prefetching, whereby it performs domain name resolution ahead of time for links included in the current page, in order to save time when links are actually clicked. This article describes how you can tune your website to disable prefetching, or to adjust how prefetching operates.

New Canvas features

HTML 5 text API for canvas elements

Canvas elements now support the HTML 5 text API.

Shadow effects in a canvas

Canvas shadow effects are now supported.


The canvas method createImageData() is now supported, allowing code to specifically create an ImageData object instead of requiring it to be done automatically. This can improve performance of other ImageData methods by preventing them from having to create the object.

moz-opaque attribute

Added the moz-opaque attribute, which lets the canvas know whether or not translucency will be a factor. If the canvas knows there's no translucency, painting performance can be optimized. See also HTMLCanvasElement.mozOpaque.

New SVG features

Applying SVG effects to HTML content

You can now apply SVG effects to HTML and XHTML content; this article describes how.

Miscellaneous new features

ICC color correction in Firefox

Firefox 3.5 now supports ICC color correction for tagged images.

The defer attribute is now supported on script elements

This attribute indicates to the browser that it may choose to continue to parse and render the page without waiting for the script to finish executing.

Other improvements

  • The Text node's wholeText property and Text.replaceWholeText() method have been implemented.
  • The property element.children has been added. It returns a collection of child elements of the given element.
  • The property HTMLElement.contentEditable is now supported, to support editable elements.
  • The Element Traversal API is now supported by the DOM Element object.
  • HTML document nodes may now be cloned using cloneNode().
  • The non-standard getBoxObjectFor() DOM method has been removed. You should be using getBoundingClientRect() instead.
  • Dispatched DOM events can now be re-dispatched. This makes Firefox 3.5 pass Acid 3 test 30.
  • Improvements have been made to DOM 2 Range handling.
  • In non-chrome scope, caught objects in exceptions are now the actual thrown object instead of an XPConnect wrapper containing the thrown object.
  • SVG ID references are now live.
  • SVG filters now work for foreignObject.
  • The GetSVGDocument() method has been added to object and iframe elements for compatibility.
  • Implicit setting of properties in object and array initializers no longer execute setters in JavaScript.
  • The gDownloadLastDir.path variable has been renamed to gDownloadLastDir.file since it refers to an nsIFile, not a path.
  • The gDownloadLastDirPath variable has been renamed to gDownloadLastDirFile since it refers to an nsIFile, not a path.
  • Starting in Firefox 3.5, you can no longer use data: bindings in chrome packages that get XPCNativeWrapper automation.

For XUL and add-on developers

If you're an extension developer, you should start by reading Updating extensions for Firefox 3.5, which offers a helpful overview of what changes may affect your extension.

New components and functionality

Supporting private browsing mode

Firefox 3.5 offers Private Browsing mode, which doesn't record the user's activities. Extensions may support private browsing following the guidelines offered by this article.

Security changes in Firefox 3.5

This article covers security-related changes in Firefox 3.5.

Theme changes in Firefox 3.5

This article covers theme-related changes in Firefox 3.5.

Monitoring Wi-Fi access points

Code with UniversalXPConnect privileges can now monitor the list of available access points, getting information on their SSIDs, MAC addresses, and signal strength. This can be used in tandem with Geolocation to offer Wi-Fi-based location service.

Notable changes and improvements

  • The XUL textbox widget now offers a search type, for use as search fields.
  • In order to support dragging and dropping tabs between windows, the browser widget now has a swapDocShells() method.
  • Added the level attribute to the panel element; this specifies whether panels appear on top of other applications, or just on top of the window the panel is contained within.
  • XUL elements now support the clientHeight, clientWidth, scrollHeight, and scrollWidth properties.
  • keyset now include a disabled attribute.
  • In addition, keysets can now be removed using the node's removeChild() method.
  • mozIStorageStatement had the initialize() method removed; consumers should use the createStatement() method instead to get a new statement object.
  • The Storage API now offers support for asynchronous requests.
  • The nsICookie2 interface now exposes the time at which cookies were created in its new creationTime attribute.
  • Added a flag to nsIProtocolHandler (URI_IS_LOCAL_RESOURCE) that is checked during chrome registration to make sure a protocol is allowed to be registered.
  • Firefox now looks for plugins in /usr/lib/mozilla/plugins on Linux, as well as the previously supported locations.
  • The plugin API has been updated to include support for private browsing mode; you may now use NPN_GetValue() to query the state of private browsing mode using the variable NPNVprivateModeBool.

New features for end users

User experience

Location aware browsing

If you choose, you may allow Firefox 3.5 to share information about your current location with websites. Firefox 3.5 can use information about the network you're connected to in order to share your location. Of course, it asks for your permission before doing so, to ensure your privacy.

Open audio and video support

Firefox 3.5 supports embedded video and audio using the open Ogg format, as well as WAV for audio. No plugins, no confusing error messages about needing to install something or other that turns out not to be available on your platform anyway.

Local data storage

Web applications can now use Web Storage's local storage capabilities to store data on your computer. This is great for anything from site preferences to more complex data.

Security and privacy

Private Browsing

Need to use someone else's computer? Switch on Private Browsing mode and nothing will be recorded about your session, including cookies, history, and any other potentially private information.

Better privacy controls

The Privacy preference pane has been completely redesigned to offer users more control over their private information. Users can choose to retain or discard anything including history information, cookies, downloads, and form field information. In addition, users can specify whether or not to include history and/or bookmarks in the location bar's automated suggestions, so you can keep private web addresses from popping up unexpectedly while typing in the location bar.


Faster JavaScript performance

JavaScript, the "J" in "AJAX," is sped up dramatically in Firefox 3.5 with the new TraceMonkey JavaScript engine. Web applications are much faster than in Firefox 3.

Faster page rendering

Web content draws faster in Firefox 3.5, thanks to technologies such as "speculative parsing." Your users don't need to know what it means, other than "it makes things draw faster."

See also