index.md

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title: Firefox 23 for developers
slug: Mozilla/Firefox/Releases/23

---

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Changes for Web developers

Security

• Mixed content blocking. Firefox will no longer load non-secure (http) resources on secure (https) pages (Firefox bug 834836).

• The standard syntax of CSP 1.0 policies are now implemented and enforced by default.

Developer Tools

• A Network Panel has been added to the developer tools. This is more detailed view than the "Net" view option in the Web Console.

• Web Console has been renamed "Console", and includes the option to filter security errors/warnings.

• The new Toolbox Options lets you disable features, change light/dark theme, or enable Chrome/Remote debugging.

HTML

• The {{HTMLElement("blink")}} element support is now completely dropped. The <blink> tag now implements the {{domxref("HTMLUnknownElement")}} interface (Firefox bug 857820).

• The range type of the {{HTMLElement("input")}} element (<input type="range">) has been switched on by default (Firefox bug 841950).

JavaScript

• The Object.defineProperty method can now be used to redefine the length property of an Array object.

• The option to disable JavaScript, including the options to allow moving windows/replace context menu, have been removed. You may still disable JavaScript by double clicking the "javascript.enabled" option in about:config.

DOM

• D3E KeyboardEvent.key is now supported, but only for non-printable keys (Firefox bug 842927).

• The title attribute of {{domxref("DOMImplementation.createHTMLDocument")}} is now optional as per updated DOM specification.

• The ability to add a sidebar panel (window.sidebar.addPanel) has been dropped (Firefox bug 691647).

• The unprefixed {{domxref("Window.requestAnimationFrame")}} and {{domxref("Window.cancelAnimationFrame")}} methods has been added (Firefox bug 704063). The unprefixed {{domxref("Window.requestAnimationFrame")}} receives a {{domxref("DOMHighResTimeStamp")}} as argument; the prefixed version receives a timestamp in milliseconds (Firefox bug 753453).

• The text argument for {{domxref("window.alert")}} and {{domxref("window.confirm")}} is now optional (Firefox bug 861605).

• The {{domxref("HTMLMediaElement.initialTime")}} property, removed from the spec, is no more supported (Firefox bug 742537).

• The {{domxref("AnimationEvent.AnimationEvent", "AnimationEvent()")}} constructor has been added (Firefox bug 848293).

• The {{domxref("AnimationEvent.pseudoElement")}} property has been implemented (Firefox bug 848293).

• The {{domxref("TransitionEvent.TransitionEvent", "TransitionEvent()")}} constructor has been added (Firefox bug 848291).

• The {{domxref("TransitionEvent.pseudoElement")}} property has been implemented (Firefox bug 848291).

• The non-standard {{domxref("TransitionEvent.initTransitionEvent()")}} and AnimationEvent.initAnimationEvent() have been removed (Firefox bug 868751).

WebRTC

• Instead of including usernames in the {{domxref("RTCIceServer.url")}} property (such as stun:[email protected]), you now need to use the new {{domxref("RTCIceServer.username")}} property.

CSS

• The blink effect for text-decoration: blink; has no more effect, but is still a valid value (Firefox bug 857820).

• In-flow {{cssxref("::after")}} and {{cssxref("::before")}} pseudo-elements are now flex items (Firefox bug 867454).

• The way to compute viewport units has been changed. In conjunction with overflow:auto, space taken by eventual scrollbars is not subtracted from the viewport, whereas in the case of overflow:scroll, it is. (Firefox bug 811403)

MathML

• Negative widths for the {{MathMLElement("mspace")}} element has been implemented (Firefox bug 717546).

• The {{MathMLElement("semantics")}} element now determines the visible child as described in the MathML3 specification.

Changes for addon and Mozilla developers

Firefox developer tools

Addons that overlay chrome://browser/content/debugger.xul must now overlay chrome://browser/content/devtools/debugger.xul. You may add references to both these files in chrome.manifest for compatibility.

See also

• Firefox 23 Aurora Notes

Older versions

{{Firefox_for_developers('22')}}