Firefox 10 for developers

• The new HTML5 <bdi> element, bi-directional isolation, allowing isolation of parts of text with a different directionality has been implemented. This is especially useful when displaying text with an unknown directionality, coming from a database for example, in the middle of text with a known, and potentially, different one.
• You may now specify a fragment of "top" for the href attribute to create a link to the top of the page. This used to work, then went away for a while, and now it's back, for compatibility with the HTML5 specification. For example: <a href="#top">Return to top of page</a>.

• The method WeakMap.set() now returns undefined, instead of itself.
• A bug was introduced in regular expression handling in Firefox 7; this has been fixed. See Firefox bug 683838 if you want the gory details.
• You can no longer use E4X syntax while in ECMAScript 5 strict mode (that is, after "use strict;").

DOM3 Events

• The DOM Event method event.stopImmediatePropagation has been implemented.
• The mouse events mouseenter and mouseleave have been implemented.

DOM4

• The attribute document.xmlVersion (which was only gettable and not settable) has been removed as it has been deprecated in the DOM4 specification. The article for document.xmlVersion now suggests a way to detect whether the document is HTML or XML without using that property.
• The attribute document.xmlStandalone has been removed as it has been deprecated in the DOM4 specification.
• The attribute document.xmlEncoding has been removed as it has been deprecated in the DOM4 specification.
• The attribute text.isElementContentWhiteSpace has been removed as it has been deprecated in the DOM4 specification.
• The method text.replaceWholeText has been removed as it has been deprecated in the DOM4 specification.
• The method node.isSameNode has been removed as it has been deprecated in the DOM4 specification. Instead of node1.isSameNode(node2), you can use the === operator, like this: node1 === node2.

Page Visibility API

• The Page Visibility API has been implemented (prefixed): document.mozHidden, document.mozVisibilityState are available and the event mozvisibilitychanged is sent when the state is modified.

Full Screen API

• Support for Document/fullscreenEnabled has been added.
• The new :-moz-full-screen-ancestor property has been added. This lets you match against elements that are ancestors of an element in full screen mode.

Battery API

• Experimental support for window.navigator.mozBattery has been added (can be enabled setting the preference dom.battery.enabled to true and will be enabled by default starting with Firefox 11).

Canvas

• The createPattern() method now throws an exception if a zero-sized source canvas is specified.
• If you use a non-finite value for any of the numeric parameters to putImageData(), the call is now silently ignored instead of throwing an exception, in keeping with the specification.

WebGL

• Firefox 10 now supports the OES_standard_derivatives extension.
• New preferences have been added to help test WebGL code for compatibility with minimally-capable devices on your full development platform.

Web Workers

• The attribute XMLHttpRequest.responseType and XMLHttpRequest.response are now available from inside Workers.
• The Worker() constructor now accepts data URLs.

IndexedDB

Great progress has been made to update IndexedDB to the latest draft specification. This effort will continue in Firefox 11.

• The IDBIndex.count() and IDBObjectStore.count() methods have been added.
• The IDBCursor.advance() method has been added.
• When encountering an unknown optional parameter in IDBObjectStore.createIndex() or IDBDatabase.createObjectStore(), Gecko will not fire an exception anymore, but ignore it.
• When IDBTransaction.abort() is called, all pending IDBRequest have their errorCode set to ABORT_ERROR.
• The methods IDBObjectStore.delete() and IDBCursor.delete() now set the result attribute of the returned IDBRequest to undefined.
• The method IDBDatabase.setVersion() has been removed as it was removed from the latest spec. The version of the database is given through the IDBFactory.open() method which has been updated and the onupgradeneeded callback allows the schema of the database to be upgraded. The version itself has been changed from a DOMString to an unsigned long long. The IDBVersionChangeRequest interface has been removed and replaced by the new IDBOpenDBRequest interface.
• When opening a database with IDBFactory.open(), if the version parameter is not provided and the database does not exist, then it will be created with a version of 1.
• The method IDBFactory.deleteDatabase() method has been added.
• Methods that search via an IDBKeyRange (such as IDBObjectStore.openCursor and IDBIndex.getKey) can accept either a single key or key range.

Other

• When the proper MIME type is passed, image/svg+xml, the DOMParser now creates a SVGDocument when given a string with SVG.
• In the past, when element.setAttribute() parsed integers, it would report an error if the integer included any non-numeric characters (for example "42foo"). Now it correctly truncates this as the number 42, in accordance with the specification.
• The ESC key no longer incorrectly results in the onkeydown handler incorrectly getting called.
• The NameList interface is no longer implemented; it previously had an implementation with no way to actually get access to one.
• The document.createProcessingInstruction() method now works on HTML documents as well as XML documents. ProcessingInstruction nodes are still only supported on XML documents, but since nodes can be moved among documents, it's helpful to be able to create them on HTML documents as well.
• The XMLHttpRequest responseType "moz-json" introduced in Firefox 9 has been updated to the latest draft of the specification and has been unprefixed. See note in Firefox bug 707142.

• CSS 3D Transforms are now supported. This includes support for the transform-style, perspective, perspective-origin and backface-visibility properties, as well as for 3D transform functions in the transform and <transform-function> properties. See Using CSS transforms for details.
• Two new values for the CSS property unicode-bidi have been added: -moz-isolation and -moz-plaintext. The -moz-isolation value isolates, from a directionality point of view, the element from its environment, letting it have a different directionality. An element with unicode-bidi:-moz-isolation behaves like a <bdi> element. The -moz-plaintext indicates the browser to use the Unicode browser heuristic to determine directionality and not the CSS direction property.
• The CSS linear-gradient() and repeating-linear-gradient() properties have been updated to support the new to syntax and the magic corner algorithm. This allows to give a precise color on the corner of a gradient-filled box.
• The text-overflow property's handling of cases in which the box overflows on both sides while the text-overflow property is set to overflow on only one has been corrected.
• Handling of the position property on elements inside positioned <table> elements has been fixed. This change will affect layout of pages; however, we now comply with the CSS specification and with other browsers, so this should be easy to fix.
• Margin collapsing around <table> elements has been fixed to match the CSS specification. Previously, table elements' margins would not be collapsed along with other adjacent elements, leading to incorrect layout. This change will affect layout of pages; however, we now comply with the CSS specification and with other browsers, so this should be easy to fix.

• The <mask> element has been updated to support both sRGB and linearRGB, and now defaults to sRGB, in compliance with the latest revision of the SVG 1.1 specification.

• The HTTP Accept-Charset header is no longer sent in HTTP requests. In its absence, servers should respond by sending UTF-8.

• The console object has two new methods, console.time() and console.timeEnd(), which can be used to set timers on a page.
• The new Page Inspector has been added, providing an excellent way to examine and manipulate the HTML and CSS behind your content.

For an overview of likely issues that may arise when updating your add-ons to support Firefox 10, see Updating add-ons for Firefox 10.

• Support for <em:strictCompatibility> has been added to the install manifest. It allows add-ons authors to opt in to checking the maximum version of their extension. If set to true the add-on will be disabled if the application version is greater than <em:maxVersion>. Firefox 10 defaults to add-ons being compatible, regardless of their specified maximum version. This flag overrides that preference. You should set this if your add-on does things that are likely to be broken by Firefox updates, but not if your add-on has a binary component, since such add-ons always get strictly checked (remember that binary components must always be recompiled for each major Firefox release).
• If you wish to revert to the old behavior — that is, to strict compatibility checking for all add-ons, regardless of the value of the strictCompatibility flag in their manifests, you can set the extensions.strictCompatibility preference to true.

• Bootstrapped add-ons using a chrome.manifest file now have the manifest file registered automatically. See the section Adding user interface with a chrome.manifest for details.

• Several new properties and methods have been added to Components.utils, granting access to assorted debugging-related information.

• The mozISpellCheckingEngine and nsIEditorSpellCheck interfaces have been updated to allow restartless add-ons to add dictionaries to the spell checker.
• The nsIBrowserHistory.lastPageVisited attribute has been removed.
• The nsIDocumentViewer interface has been merged into nsIContentViewer.
• The nsIURIFixup interface has a new flag, FIXUP_FLAG_USE_UTF8, which lets you tell it to use UTF-8 instead of the platform character set, when doing conversions.

• The new variable NPNVdocumentOrigin has been added; this returns the document origin, and is more secure than window.location.

• The --disable-rdf build option, which actually made it impossible to successfully build, has been removed. Work is ongoing on being able to actually remove RDF support entirely, but at present XUL still requires it to function. See Firefox bug 559505 for progress on removing the last vestiges of RDF being required.
• The --disable-smil build option has been removed.

• Firefox 9 for developers
• Firefox 8 for developers
• Firefox 7 for developers
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• Firefox 5 for developers
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• Firefox 3.6 for developers
• Firefox 3.5 for developers
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• Firefox 1.5 for developers