index.md

---

title: Firefox 31 for developers
slug: Mozilla/Firefox/Releases/31

---

{{FirefoxSidebar}}

Changes for Web developers

Developer Tools

Highlights:

• Eyedropper tool to select colors in web pages

• full stack traces for console error messages

• editable Box Model View

• %c formatting to style console messages

• "copy as cURL" command in Network Monitor

• Sublime Text keybindings in the source editor

• Option to make Network Monitor logs persistent

• JavaScript warnings on by default in the Web Console

• Alt+click to expand all descendants of a node

All devtools bugs fixed between Firefox 30 and Firefox 31.

CSS

• Changed var- prefix of CSS Variables to -- to reflect the final spec change (Webkit bug 985838).

• The {{cssxref("hyphens")}} property now support Polish hyphenation rules (Webkit bug 987668).

• Removed an unwanted white space for multiple of 10,000 in Korean counter styles (Webkit bug 985186).

• CSS opacity transition broken with parent pseudo :before and overflow auto (Webkit bug 990340).

• The ::-moz-math-stretchy pseudo-element has been removed (Webkit bug 1000879).

HTML

• {{HTMLElement("track")}} has been implemented (Webkit bug 629350).

JavaScript

New ECMAScript 2015 features implemented:

• New Array built-in: {{jsxref("Array.prototype.fill()")}} (Webkit bug 911147)

• New Math function: {{jsxref("Math.clz32()")}} (Webkit bug 925123)

• New String built-in: {{jsxref("String.prototype.normalize()")}} is available in Firefox Desktop (Webkit bug 918987).

• New Object method {{jsxref("Object.setPrototypeOf()")}}.

• New Number constants: {{jsxref("Number.MAX_SAFE_INTEGER")}} and {{jsxref("Number.MIN_SAFE_INTEGER")}}.

• The ES2015 Proxy {{jsxref("Global_Objects/Proxy/Proxy/isExtensible", "isExtensible")}} trap have been implemented (Firefox bug 978235).

Interfaces/APIs/DOM

• Constructor of KeyboardEvent has been implemented (Webkit bug 930893).

• The Resource Timing API has been implemented (see Webkit bug 822480).

• KeyboardEvent.isComposing attribute has been implemented (Webkit bug 993234).

• InputEvent interface has been implemented (Webkit bug 993253).

• InputEvent.isComposing attribute has been implemented (Webkit bug 993253).

• {{domxref("CSS.escape", "CSS.escape()")}} has been implemented (Webkit bug 955860).

• {{domxref("Element/mousemove_event", "mousemove")}} is now cancelable like in other browsers (Webkit bug 704423). Calling preventDefault() only sets defaultPrevented attribute to true; any other behaviors are not changed. E.g., it cannot prevent to set :hover state.

• The {{domxref("Path2D")}} interface has been implemented.

• The {{domxref("CanvasRenderingContext2D.isPointInPath()")}}, {{domxref("CanvasRenderingContext2D.isPointInStroke()")}}, {{domxref("CanvasRenderingContext2D.clip()")}}, {{domxref("CanvasRenderingContext2D.fill()")}} and {{domxref("CanvasRenderingContext2D.stroke()")}} methods have been updated to optionally accept a {{domxref("Path2D")}} object.

• Implemented {{domxref("HTMLMediaElement.fastSeek()")}}.

• The Connection interface has been renamed to {{domxref("NetworkInformation")}} and has been modified to match the new specification (Firefox bug 960426).

• The {{domxref("Navigator.sendBeacon()")}} has been implemented; this allows asynchronous transmission of analytics or other data in a manner that doesn't rely on the transmitting page remaining loaded, so that it can be used in an {{domxref("Window/unload_event", "unload")}} or {{domxref("Window.beforeunload_event", "beforeunload")}} handler.

MathML

• Partial implementation of the OpenType MATH table, section 6.3.6 (Webkit bug 407059). For details, try the MathML torture test .

• The ::-moz-math-stretchy pseudo-element has been removed (Webkit bug 1000879).

• When available, the Unicode Mathematical alphanumeric characters are used for bold, italic and bold-italic math variants (Webkit bug 930504).

SVG

No change.

Audio/Video

No change.

Security

• Privileged code now gets Xray vision for Date instances.

Changes for add-on and Mozilla developers

• The "align" attribute on the urlbar-wrapper (formerly on the urlbar-container) which was set to "center" since time immemorial, has been removed. This is known to affect third-party themes. You should look carefully at what the right fix is for your theme, but for maintaining the equivalent effect, you can add the following CSS rule to your theme:

  #urlbar-wrapper {
    -moz-box-align: center;
  }
  

• nsIDOMWindowUtils.sendQueryContentEvent() and nsIDOMWindowUtils.sendSelectionSetEvent() have aAdditionalFlags as optional argument. If you called nsIDOMWindowUtils.sendSelectionSetEvent() with true for aReverse, the behavior would be broken by this change. See explanation of each flag (QUERY_CONTENT_FLAG_* and SELECTION_SET_FLAG_*) for the detail of aAdditionalFlags.

Add-on SDK

Highlights:

• Add-on Debugger

• Added the ability to convert between high-level BrowserWindow objects and DOM windows, and between high-level Tab objects and XUL tabs.

• Updated the default theme used for panels on Mac OS X.

• Added contentStyle and contentStyleFile options to panel.

GitHub commits made between Firefox 30 and Firefox 31. This will not include any uplifts made after this release entered Aurora.

Bugs fixed between Firefox 30 and Firefox 31. This will not include any uplifts made after this release entered Aurora.

Older versions

{{Firefox_for_developers('30')}}