Firefox 26 for developers

• The text-decoration-line property, still prefixed, now considers 'blink' as a valid value, though it doesn't blink the content at all (Firefox bug 812995).
• The non-standard -moz-text-blink property has been removed (Firefox bug 812995).
• Support for the image-orientation property, in its CSS Images & Values Level 4 version, that is with the from-image keyword and EXIF support, has been added (Firefox bug 825771).
• Experimental support for position: sticky has been implemented and can be enabled by pref layout.css.sticky.enabled (Firefox bug 886646).
• The text-align property now applies to the ::-moz-placeholder pseudo-element (Firefox bug 915551).

• The HTMLSelectElement.selectedOptions property has been implemented (Firefox bug 596681).
• In the <input> element of type email, values with domain labels longer than 63 chars are no more considered valid (Firefox bug 884332).
• The HTMLInputElement.width and height properties now return 0 when the type is not image (Firefox bug 905240).
• A <fieldset> element is now invalid, and can be styled using the :invalid pseudo-class, when one of the elements it contains is invalid (Firefox bug 717181).

ECMAScript 2015 implementation continues!

• The ECMAScript 2015 compliant syntax for Generators (yield) has been implemented (Firefox bug 666399).
• Generator/Iterator results are now boxed like { value: foo, done: bool } (Firefox bug 907744).
• New mathematical methods have been implemented on Math: Math.fround() (Firefox bug 900125).
• The reserved words cannot be used for function names:such a usage now throws a SyntaxError (Firefox bug 907958).
• The default parameter syntax has been updated to allow parameters without defaults after default parameters, such as function f(x=1, y). See Firefox bug 777060.
• GeneratorFunction is implemented (Firefox bug 904701).

• Make the last argument (doctype) to DOMImplementation.createDocument optional (Firefox bug 909859).
• Implement the new element.classList specification which permits adding/removing several classes with one call (Firefox bug 814014).
• The URL() constructor has been implemented on the URL interface (Firefox bug 887364).
• The properties URLUtils.origin, URLUtils.password, and URLUtils.username are now available to all interfaces implementing URLUtils: URL, Location, HTMLAnchorElement, and HTMLAreaElement (Firefox bug 887364).
• The URL interface is now accessible from Web Workers (Firefox bug 887364).
• IndexedDB can now be used as a "optimistic" storage area so it doesn't require any prompts and data is stored in a pool with LRU eviction policy, in short temporary storage (Firefox bug 785884).
• Support for WaveShaperNode.oversample has been added (Firefox bug 875277).
• Path of the persistent storage has been changed from <profile>/indexedDB to <profile>/storage/persistent (on b2g from /data/local/indexedDB to /data/local/storage/persistent).
• The Screen.orientation property and Screen.lockOrientation() method now support the default value, mapping to portrait-primary or landscape-primary, depending of the device (Firefox bug 908058) This works only for Firefox OS and Firefox for Android. Firefox Desktop is not supported.
• Event constructors can be used in Web workers (Firefox bug 910910).
• Trying to set the Document.domain property on a page embedded in an <iframe> with the sandbox attribute now throws a security error (Firefox bug 907892).
• The MessageEvent interface has been updated to comply with the latest spec. The initMessageEvent method has been removed while the interface has now a constructor (Firefox bug 848294).
• The HTML5 MessageChannel API has been implemented, behind the dom.messageChannel.enabled preference (Firefox bug 677638).
• Support for VTTCue, behind the media.webvtt.enabled preference, like for all WebVTT-related implementations, has been added (Firefox bug 868509).
• The Web Audio API has been made available by default (Firefox bug 885505).

• Inconsistent renderings of <mmultiscripts>, <msub>, <msup> and <msubsup> have been unified and the error handling of these elements has been improved (Firefox bug 827713).

• The inclusion of SVG glyphs inside OpenType, SVG-in-OpenType, has been updated to match the current version of the specification (Firefox bug 906521).
• The SVGElement.ownerSVGElement() method doesn't throw anymore (Firefox bug 835048).

• The Inspector is now remotable (Firefox bug 805526).
• The web console text can be selected, ::before and ::after now inspectable, debugger and responsive design features are planned for this release. (https://hacks.mozilla.org/2013/09/new-features-in-the-firefox-developer-tools-episode-26/)