---
title: Firefox 30 for developers
slug: Mozilla/Firefox/Releases/30
translation_of: Mozilla/Firefox/Releases/30
original_slug: Mozilla/Firefox/เปิดผนึก/30
---
<div>{{FirefoxSidebar}}</div><p>Want to help document Firefox 30? See the <a class="external" href="http://beta.elchi3.de/doctracker/#list=fx&amp;version=30.0">list of bugs that need to be written about</a> and pitch in!</p>
<h2 id="Changes_for_Web_developers">Changes for Web developers</h2>
<h3 id="Developer_Tools">Developer Tools</h3>
<ul>
 <li>A Box Model Highlighter has been implemented ({{bug(663778)}}).</li>
 <li>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 <a href="http://www.robodesign.ro/mihai/blog/web-console-improvements-episode-30">blog post</a>.</li>
 <li>Support for {{domxref("Console.count()")}} has been added ({{bug(922208)}}).</li>
</ul>
<h3 id="CSS">CSS</h3>
<ul>
 <li>The property {{cssxref("background-blend-mode")}} has been enabled by default ({{bug(970600)}}).</li>
 <li>The non-standard {{cssxref("overflow-clip-box")}} property has been implemented for use in UA stylesheets only ({{bug(966992)}}).</li>
 <li>The {{cssxref("line-height")}} property now affects single-line text inputs (<code>&lt;input type=text|password|email|search|tel|url|unknown&gt;</code> types) although it cannot shrink them below a line height of <code>1.0</code> ({{bug(349259)}}).</li>
 <li>The {{cssxref("line-height")}} property now also affects <code>type=button</code>, with no restrictions ({{bug(697451)}}).</li>
 <li>Change to keyframes' name does not affect current elements ({{bug(978648)}}).</li>
</ul>
<h3 id="HTML">HTML</h3>
<p><em>No change.</em></p>
<h3 id="JavaScript">JavaScript</h3>
<ul>
 <li>New ES6-compatible <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Array_comprehensions">array comprehensions</a> <code>[for (item of iterable) item]</code> and <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Generator_comprehensions">generator comprehensions</a> <code>(for (item of iterable) item)</code> have been implemented ({{bug(979865)}}).</li>
 <li>Typed arrays are now extensible and support new named properties ({{bug(695438)}}).</li>
 <li>The {{jsxref("Error.prototype.stack")}} property now contains column numbers ({{bug(762556)}}) and has been improved <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/Stack#Stack_of_eval'ed_code">when using <code>Function()</code> and <code>eval()</code> calls</a>. This can help you to better debug minified or generated JavaScript code.</li>
</ul>
<h3 id="InterfacesAPIsDOM">Interfaces/APIs/DOM</h3>
<ul>
 <li>{{domxref("Navigator.sendBeacon")}} has been implemented, easing telemetry collection ({{bug(936340)}}).</li>
 <li>Added a <code>relList</code> property returning a {{domxref("DOMTokenList")}} to {{domxref("HTMLLinkElement")}}, {{domxref("HTMLAreaElement")}} and {{domxref("HTMLAnchorElement")}} ({{bug(968637)}}).</li>
 <li>As per the latest specification, the first argument of {{domxref("OscillatorNode.start")}} and {{domxref("OscillatorNode.stop")}} is now optional and defaults to <code>0</code> ({{bug(982541)}}).</li>
 <li>The method {{domxref("Navigator.requestWakeLock()")}} and the non-standard {{domxref("MozWakeLock")}} are no longer available from the Web on Desktop ({{bug(963366)}}).</li>
 <li>The <code>DOM_VK_ENTER</code> constant has been removed from {{domxref("KeyboardEvent")}} ({{bug(969247)}}).</li>
 <li>Web components' {{domxref("Document.register")}} has been adapted to follow the behavior described in the latest version of the specification ({{bug(856140)}}).</li>
 <li>Basic support for Hit regions on canvas has been added: the methods {{domxref("CanvasRenderingContext2D.addHitRegion()")}} and {{domxref("CanvasRenderingContext2D.removeHitRegion()")}} have been added. These are disabled by default; to activate them set the preference <code>canvas.hitregions.enabled</code> to <code>true</code>. ({{bug(966591)}})</li>
 <li>The non-standard, and deprecated since Firefox 15, {{domxref("Blob.mozSlice")}} is no longer supported ({{bug(961804)}}).</li>
 <li>The non-standard {{domxref("ArchiveReader")}} and {{domxref("ArchiveRequest")}} are no longer exposed to the Web ({{bug(968883)}}).</li>
 <li><a href="http://dxr.mozilla.org/mozilla-central/source/dom/webidl/">WebIDL constructors</a> cannot be called as functions anymore. They need to be preceded by the keyword <code>new</code>. ({{bug(916644)}})</li>
 <li>Added support for a new value (<code>alpha</code>) for the second, optional, parameter of the {{domxref("Canvas.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 <code>1.0</code>. This allows the back-end to implement a fast-track. ({{bug(982480)}})</li>
</ul>
<h3 id="MathML">MathML</h3>
<p><em>No change.</em></p>
<h3 id="SVG">SVG</h3>
<ul>
 <li>{{SVGElement("feDropShadow")}}, and its interface {{domxref("SVGFEDropShadowElement")}}, from the Filter Effects Module are now supported ({{bug(964200)}}).</li>
</ul>
<h3 id="AudioVideo">Audio/Video</h3>
<ul>
 <li>On Linux, Gstreamer 1.0 is now supported (instead of 0.10) ({{bug(806917)}}).</li>
</ul>
<h2 id="Security">Security</h2>
<p><em>No change.</em></p>
<h2 id="Changes_for_add-on_and_Mozilla_developers">Changes for add-on and Mozilla developers</h2>
<ul>
 <li>The interface <code>nsIDOMWindowUtils</code> now supports the Boolean attribute <code>audioMuted</code> and <code>audioVolume</code>, a float in the range <code>[0.0</code> ,  <code>1.0]</code>, 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)}})</li>
</ul>
<h2 id="See_also">See also</h2>
<ul>
 <li><a href="/en-US/docs/Mozilla/Firefox/Releases/30/Site_Compatibility">Site Compatibility for Firefox 30</a></li>
</ul>
<h3 id="Older_versions">Older versions</h3>
<p>{{Firefox_for_developers('29')}}</p>