---
title: Firefox 19 para Desarrolladores
slug: Firefox_19_para_desarrolladores
translation_of: Mozilla/Firefox/Releases/19
---
<div>{{FirefoxSidebar}}</div>

<p>
 </p><p>Quieres ayudar a documentar Firefox 19? Visita la <a class="external" href="http://beta.elchi3.de/doctracker/#list=fx&amp;version=19.0">lista de bugs que necesitan ser revisados</a> e inicia!</p>
<p></p>

<h2 id="Cambios_para_desarrolladores">Cambios para desarrolladores</h2>

<h3 id="JavaScript">JavaScript</h3>

<ul>
 <li>Los objetos <code style="font-size: 14px;"><a href="/en-US/docs/JavaScript/Reference/Global_Objects/Map" title="/en-US/docs/JavaScript/Reference/Global_Objects/Map">Map</a> y</code> <code><a href="/en-US/docs/JavaScript/Reference/Global_Objects/Set" title="/en-US/docs/JavaScript/Reference/Global_Objects/Set">Set</a></code> pasaron de tener un método <code>size()</code> a tener una propiedad <code>size</code> ({{bug("807001")}})</li>
 <li>Los objetos <a href="/en-US/docs/JavaScript/Reference/Global_Objects/Map" style="font-family: 'Courier New', 'Andale Mono', monospace; line-height: normal;" title="/en-US/docs/JavaScript/Reference/Global_Objects/Map">Map</a> and <code><a href="/en-US/docs/JavaScript/Reference/Global_Objects/Set" title="/en-US/docs/JavaScript/Reference/Global_Objects/Set">Set</a></code> ahora tienen un método clear(). ({{bug("805003")}})</li>
</ul>

<h3 id="CSS">CSS</h3>

<ul>
 <li>Support for the viewport-relative {{cssxref("&lt;length&gt;")}} units, <code>vh</code>, <code>vw</code>, <code>vmin</code>, and <code>vmax</code>, has landed ({{bug("503720")}})</li>
 <li>CSS Flexbox has been unprefixed, but remains disabled by default ({{bug("801098")}}).</li>
 <li>The <code>-moz-initial</code> value has been unprefixed ({{bug("806068")}}). <code>-moz-initial</code> will be kept for a while as an alias; however, authors are strongly encouraged to switch over to <code>initial</code>.</li>
 <li>The CSS {{ cssxref("text-transform")}} property now supports the <code>full-width</code> keyword, which allows a more seamless inclusion of Latin characters in text using ideographic fixed-width characters, like Chinese or Japanese ({{bug("774560")}}).</li>
 <li>The CSS {{ cssxref("page-break-inside")}} has been implemented ({{bug("685012")}}).</li>
 <li>The CSS {{ cssxref("calc", "calc()")}} function can now be used on <code>&lt;color-stop&gt;</code> (on {{cssxref("&lt;gradient&gt;")}}).</li>
 <li>The CSS {{ cssxref("@page") }} at-rule is now supported ({{bug("115199")}}). Note that the pseudo-classes {{cssxref(":first")}}, {{cssxref(":right")}}, and {{cssxref(":left")}} are not yet implemented.</li>
 <li>The {{ cssxref(":-moz-placeholder") }} pseudo-class is replaced by the {{ cssxref("::-moz-placeholder") }} pseudo-<em>element</em> ({{ bug("737786") }}).</li>
</ul>

<h3 id="DOM">DOM</h3>

<ul>
 <li>The {{ domxref("element.getElementsByTagName") }} method will now return <code>HTMLCollection</code> ({{bug("799464")}}).</li>
 <li>The {{domxref("File")}} <code>mozLastModifiedDate</code> property has been implemented. ({{bug("793955")}})</li>
 <li>The {{domxref("CanvasRenderingContext2D")}} <code>isPointInStroke</code> method has been implemented ({{bug("803124")}}).</li>
</ul>

<h3 id="XForms">XForms</h3>

<p>Support for <a href="/en-US/docs/XForms" title="/en-US/docs/XForms">XForms</a> has been <a href="http://www.philipp-wagner.com/blog/2011/07/the-future-of-mozilla-xforms/" title="http://www.philipp-wagner.com/blog/2011/07/the-future-of-mozilla-xforms/"><strong>removed</strong></a> in Firefox 19.</p>

<h2 id="Changes_for_add-on_and_Mozilla_developers">Changes for add-on and Mozilla developers</h2>

<div class="note">
<p><strong>Note:</strong> A key change in Firefox 19 is that <a href="/en-US/docs/XPCOM_API_Reference/nsresult" title="/en-US/docs/XPCOM_API_Reference/nsresult"><code>nsresult</code></a> is now strongly typed. This will help make it easier to detect bugs that are caused by mishandling of return values, but may cause existing code to break if it's making incorrect assumptions in this regard.</p>
</div>

<ul>
 <li><code>getBrowserSelection()</code> now returns the selected text in a text input field. As a result, <code>gContextMenu.isTextSelected</code> will be <code>true</code> when the user selects text in a text input field that is not a password field. ({{bug("565717")}})</li>
 <li><a href="/en/Mozilla/JavaScript_code_modules/Dict.jsm" title="en/Mozilla/JavaScript_code_modules/Dict.jsm">Dict.jsm</a>: <a href="/en/Mozilla/JavaScript_code_modules/Dict.jsm#Creating_a_dictionary" title="en/Mozilla/JavaScript_code_modules/Dict.jsm#Creating_a_dictionary"><code>Dict()</code></a> now takes a JSON String. <a href="/en/Mozilla/JavaScript_code_modules/Dict.jsm#toJSON()" title="en/Mozilla/JavaScript_code_modules/Dict.jsm#toJSON()"><code>Dict.toJSON()</code></a> was added, and it returns a JSON String. ({{bug("727967")}})</li>
</ul>

<h2 id="See_also">See also</h2>

<ul>
 <li><a href="http://www.mozilla.org/en-US/firefox/19.0beta/releasenotes/">Firefox 19 Beta Release Notes</a></li>
 <li><a href="/en-US/docs/Site_Compatibility_for_Firefox_19">Site Compatibility for Firefox 19</a></li>
</ul>

<h3 id="Older_versions">Older versions</h3>

<p>{{Firefox_for_developers('18')}}</p>