Firefox 30 for developers

• A Box Model Highlighter has been implemented (bug 663778).
• Anywhere a DOM node appears in the console output, it is highlighted when you hover over that console output (bug 757866). Similarly all JS functions and objects are highlighted in the console output (bug 584733). More information about the console improvement can be found in this blog post.
• Support for console.count() has been added (bug 922208).

• The property background-blend-mode has been enabled by default (bug 970600).
• The non-standard overflow-clip-box property has been implemented for use in UA stylesheets only (bug 966992).
• The line-height property now affects single-line text inputs (<input type=text|password|email|search|tel|url|unknown> types) although it cannot shrink them below a line height of 1.0 (bug 349259).
• The line-height property now also affects type=button, with no restrictions (bug 697451).
• Change to keyframes' name does not affect current elements (bug 978648).
• positioned internal table elements not abs pos containing block(relative position for table rows) (bug 63895).

No change.

• New ES2015-compatible array comprehensions [for (item of iterable) item] and generator comprehensions (for (item of iterable) item) have been implemented (bug 979865).
• Typed arrays are now extensible and support new named properties (bug 695438).
• The Error.prototype.stack property now contains column numbers (bug 762556) and has been improved when using Function() and eval() calls. This can help you to better debug minified or generated JavaScript code.
• The Promise.cast() method has been renamed to Promise.resolve() (bug 966348).

• Navigator.sendBeacon has been implemented, easing telemetry collection (bug 936340).
• Added a relList property returning a DOMTokenList to HTMLLinkElement, HTMLAreaElement and HTMLAnchorElement (bug 968637).
• As per the latest specification, the first argument of OscillatorNode.start and OscillatorNode.stop is now optional and defaults to 0 (bug 982541).
• The method Navigator.requestWakeLock() and the non-standard MozWakeLock are no longer available from the Web on Desktop (bug 963366).
• The DOM_VK_ENTER constant has been removed from KeyboardEvent (bug 969247).
• Web components' Document.register has been adapted to follow the behavior described in the latest version of the specification (bug 856140).
• The non-standard, and deprecated since Firefox 15, Blob.mozSlice is no longer supported (bug 961804).
• The non-standard ArchiveReader and ArchiveRequest are no longer exposed to the Web (bug 968883).
• WebIDL constructors cannot be called as functions anymore. They need to be preceded by the keyword new. (bug 916644)
• Added support for a new value (alpha) for the second, optional, parameter of the HTMLCanvasElement.getContext() method allowing to define if alpha blending must be stored or not for this context. When not, the per-pixel alpha value in this store is always 1.0. This allows the back-end to implement a fast-track. (bug 982480)
• GlobalWorkerScope.console now returns for the regular console; WorkerConsole has been removed (bug 965860).
• The WebGL_debug_shaders WebGL extension has been implemented (bug 968374).

No change.

• <feDropShadow>, and its interface SVGFEDropShadowElement, from the Filter Effects Module are now supported (bug 964200).

• On Linux, Gstreamer 1.0 is now supported (instead of 0.10) (bug 806917).

No change.

• The interface nsIDOMWindowUtils now supports the Boolean attribute audioMuted and audioVolume, a float in the range [0.0 , 1.0], allowing to control the sound produced by a window (that is any tab or iframe). There is no UI for this, but is available to add-ons. (bug 923247)