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Firefox 3.6 offers support for new and developing web standards, increased performance, and an overall better experience for web users and developers. This page provides links to articles covering the new capabilities of Firefox 3.6.

For web site and application developers


Using gradients
Firefox 3.6 adds support for the proposed -moz-linear-gradient and -moz-radial-gradient properties for background.
Multiple backgrounds
The background property (as well as background-color, background-image, background-position, background-repeat, and background-attachment) now supports multiple backgrounds. This lets you specify multiple backgrounds that are rendered atop one another in layers.
Mozilla-specific media features
Media features have been added for Mozilla-specific system metrics, so that media queries can be used to more safely check on the availability of features such as touch support.
Scaling background images
The background-size property from the CSS 3 Backgrounds and Borders draft is now supported under the name -moz-background-size.
WOFF font support
@font-face now supports the WOFF downloadable font file format.
Pointer events
The pointer-events property lets content specify whether or not an element may be the target of mouse pointer events.

Miscellaneous CSS changes


Using files from web applications
Support for the new HTML5 File API has been added to Gecko, making it possible for web applications to access local files selected by the user. This includes support for selecting multiple files using the input type="file" HTML element's new multiple attribute.
HTML5 video supports poster frames
The poster attribute is now supported for the video element, allowing content to specify a poster frame to be displayed until the video begins to play.
Checkboxes and radio buttons support the indeterminate property
HTML input elements of types checkbox and radio now support the indeterminate property, which allows a third, "indeterminate" state.
Canvas image smoothing can be controlled
The new mozImageSmoothingEnabled property can be used to turn on and off image smoothing when scaling in canvas elements.
Asynchronous script execution
By setting the async attribute on a script element, the script will not block loading or display of the rest of the page. Instead the script executes as soon as it is downloaded.


Gecko 1.9.2 introduces JavaScript 1.8.2, which adds a number of language features from the ECMAScript 5 standard:

  • Date.parse() can now parse ISO 8601 dates like YYYY-MM-DD.
  • The prototype property of function instances is no longer enumerable.


Web workers can now self-terminate
Workers now support the nsIWorkerScope.close() method, which allows them to terminate themselves.
Drag and drop now supports files
The DataTransfer object provided to drag listeners now includes a list of files that were dragged.
Checking to see if an element matches a specified CSS selector
The new element.mozMatchesSelector method lets you determine whether or not an element matches a specified CSS selector. See bug 518003.
Detecting device orientation
Content can now detect the orientation of the device if it has a supported accelerometer, using the MozOrientation event. Firefox 3.6 supports the accelerometer in Mac laptops.
Detecting document width and height changes
The new MozScrollAreaChanged event is dispatched whenever the document's scrollWidth and/or scrollHeight properties change.

Miscellaneous DOM changes

  • The getBoxObjectFor() method has been removed, as it was non-standard and exposed even more non-standard stuff to the web. See bug 340571. Also affects MooTools which uses this call for Gecko detection; this has been fixed in the latest version of MooTools, so be sure to update.
  • The new mozInnerScreenX and mozInnerScreenY properties on DOM windows have been added; these return the screen coordinates of the top-left corner of the window's viewport.
  • The new mozScreenPixelsPerCSSPixel attribute on the nsIDOMWindowUtils interface, accessible only to chrome, provides a conversion factor between CSS pixels and screen pixels; this value can vary based on the zoom level of the content.
  • When the page's URI's document fragment identifier (the part after the "#" (hash) character) changes, a new hashchange event is sent to the page. See window.onhashchange for more information. bug 385434
  • The attribute document.readyState is now supported. bug 347174
  • Support for HTML5's element.classList to allow easier handling of the class attribute. bug 501257
  • localName and namespaceURI in HTML documents now behave like they do in XHTML documents: localName returns in lower case and namespaceURI for HTML elements is "".
  • element.getElementsByTagNameNS no longer lowercases its argument, so upper-case ASCII letters in the argument make matches against HTML elements fail. The same is true for document.getElementsByTagNameNS.
  • Support has been added for addresses in geolocation via the nsIDOMGeoPositionAddress interface and a new field added to nsIDOMGeoPosition.
  • The window.getComputedStyle function now returns quotes within url() values.


The choose() XPath method is now supported
The choose() method is now supported by our implementation of XPath.

For XUL and add-on developers

If you're an extension developer, you should start by reading Updating extensions for Firefox 3.6, which offers a helpful overview of what changes may affect your extension. Plug-in developers should read Updating plug-ins for Firefox 3.6.

New features

Detecting device orientation
Content can now detect the orientation of the device if it has a supported accelerometer, using the MozOrientation event. Firefox 3.6 supports the accelerometer in Mac laptops.
Monitoring HTTP activity
You can now monitor HTTP transactions to observe requests and responses in real time.
Working with the Windows taskbar
It's now possible to customize the appearance of windows in the taskbar in Windows 7 or later. This has been disabled by default in Firefox 3.6.



Locale-aware collation of data is now supported by the Storage API
Gecko 1.9.2 added several new collation methods to provide optimized collation (sorting) of results using locale-aware techniques.
Properties on a statement can now be enumerated
You can now use a enumeration to enumerate all the properties on a statement.
mozIStorageStatement's getParameterIndex changed behavior between 3.5 and 3.6.
See bug 528166 for details.
Asynchronously bind multiple sets of parameters and execute a statement.
See bug 490085 for details. Documentation coming soon.



See Updating themes for Firefox 3.6 for a list of changes related to themes.

Lightweight themes
Firefox 3.6 supports lightweight themes; these are easy-to-create themes that simply apply a background to the top (URL bar and button bar) and bottom (status bar) of browser windows. This is an integration of the existing Personas theme architecture into Firefox.


  • Firefox will no longer load third-party components installed in its internal components directory. This helps to ensure stability by preventing buggy third-party components from being executed. Developers that install components this way must repackage their components as XPI packages so they can be installed as standard add-ons.
  • contents.rdf is no longer supported for registering chrome in extensions. You must now use the chrome.manifest file instead. See bug 492008.
  • Added support for hiding the menu bar automatically. See bug 477256.
  • Added support for the container-live-role attribute to objects. See bug 391829.
  • The tabs-closebutton binding has been removed. See bug 500971.
  • Added support to nsISound for playing sounds based on events that have occurred. See bug 502799.
  • The syntax for the nsITreeView methods nsITreeView.canDrop() and nsITreeView.drop() has changed to support the new drag & drop API introduced in Gecko 1.9. See bug 455590.
  • Added support to snap the mouse cursor to the default button of dialog or wizard on Windows, see bug 76053. This is processed automatically by dialog and wizard element. But if a XUL application creates a window using the window element and it has a default button, it needs to call nsIDOMChromeWindow.notifyDefaultButtonLoaded() during the window's onload event handler.
  • The nsILocalFileMac interface has had two methods removed: setFileTypeAndCreatorFromMIMEType() and setFileTypeAndCreatorFromExtension().
  • The new NetUtils.jsm code module provides an easy-to-use method for asynchronously copying data from an input stream to an output stream.
  • The new openLocationLastURL.jsm code module makes it easy to read and change the value of the "Open Location" dialog box's remembered URL while properly taking private browsing mode into account.
  • On Windows, the nsIScreen interface now reports 24 bit per pixel color depths when the graphics driver claims 32 bits, since 24 more accurately represents the actual number of color pixels in use.
  • Menu bars can now be hidden on Windows, using the new autohide attribute on the toolbar XUL element.
  • The loadOneTab and addTab methods now accept a new relatedToCurrent parameter and, in addition, allow the parameters to be specified by name, since nearly all of the parameters are optional.
  • The "hidden" property is no longer supported in install manifests; it's no longer possible to prevent the user from seeing add-ons in the add-on manager window.
  • The;1 component no longer exists; you need to use;1 instead.
  • You can now register with the update-timer category to schedule timer events without having to instantiate the object that the timer will eventually call into; it will instead be instantiated when it's needed. See nsIUpdateTimerManager.registerTimer() for details.
  • The NPN_GetValue() function no longer provides access to XPCOM through the variable values NPNVserviceManager, NPNVDOMelement, and NPNVDOMWindow. This is part of the work toward making plugins run in separate processes in a future version of Gecko.
  • Plugins are no longer scriptable through XPCOM (IDL) interfaces, NPRuntime is the API to use for making plugins scriptable, and NPP_GetValue() is no longer called to with the value NPPVpluginScriptableInstance or NPPVpluginScriptableIID. This is part of the work toward making plugins run in separate processes in a future version of Gecko.

For Firefox/Gecko developers

Certain changes are only really interesting if you work on the internals of Firefox itself.

Interfaces merged

The following interfaces have been combined together:

  • nsIPluginTagInfo2 has been merged into nsIPluginTagInfo.
  • nsIPluginInstanceInternal, nsIPPluginInstancePeer, nsIPluginInstancePeer1, nsIPluginInstancePeer2, and nsIPluginInstancePeer3 have all been merged into nsIPluginInstance.
  • nsIWindowlessPlugInstPeer has been merged into nsIPluginInstance.
  • nsIPluginManager and nsIPluginManager2 have been merged into nsIPluginHost.

Interfaces removed

The following interfaces have been removed entirely because they were unused, unimplemented, or obsolete:

  • nsIFullScreen
  • nsIDOMSVGListener
  • nsIDOMSVGZoomListener
  • nsIInternetConfigService
  • nsIDKey
  • nsIEventHandler
  • nsIJRILiveConnectPIPeer
  • nsIJRILiveConnectPlugin
  • nsIScriptablePlugin
  • nsIClassicPluginFactory
  • nsIFileUtilities

Interfaces moved

The following interfaces have been relocated from their previous IDL files into new ones:

  • nsIDOMNSCSS2Properties is now located in its own IDL file (dom/interfaces/css/nsIDOMCSS2Properties.idl).
  • nsIUpdateTimerManager is now located in its own IDL file.

A large number of interfaces have been moved. See Interfaces moved in Firefox 3.6 for a complete list.

Other interface changes

The following assorted changes have been made:

  • The nsIPlugin interface now inherits from nsISupports instead of nsIFactory.
  • The nsIPluginHost interface now inherits from nsISupports instead of nsIFactory.
  • The nsIFrame interface now inherits from nsQueryFrame instead of nsISupports.
  • The nsIDeviceContext method getPaletteInfo() has been removed, as it was never implemented.
  • The nsIScriptContext method reportPendingException() has been removed, since it was no longer being used.

Changes in accessibility code

See also