Firefox 23 for developers

Want to help document Firefox 23? See the list of bugs that need to be written about and pitch in!

Changes for Web developers

Security

• Mixed content blocking. Firefox will no longer load non-secure (http) resources on secure (https) pages (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 <blink> element support is now completely dropped. The <blink> tag now implements the HTMLUnknownElement interface (bug 857820).
• The range state of the <input> element (<input type="range">) has been switched on by default (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 (bug 842927).
• The title attribute of DOMImplementation.createHTMLDocument is now optional as per updated DOM specification.
• The ability to add a sidebar panel (window.sidebar.addPanel) has been dropped (bug 691647).
• The unprefixed Window.requestAnimationFrame and Window.cancelAnimationFrame methods has been added (bug 704063).
• The callback for Window.requestAnimationFrame now receives a DOMHighResTimeStamp as argument instead of the less precise DOMTimeStamp used in the unprefixed version (bug 753453).
• The text argument for window.alert and window.confirm is now optional (bug 861605).
• The HTMLMediaElement.initialTime property, removed from the spec, is no more supported (bug 742537).
• The AnimationEvent() constructor has been added (bug 848293).
• The AnimationEvent.pseudoElement property has been implemented (bug 848293).
• The TransitionEvent() constructor has been added (bug 848291).
• The TransitionEvent.pseudoElement property has been implemented (bug 848291).
• The non-standard TransitionEvent.initTransitionEvent() and AnimationEvent.initAnimationEvent() have been removed (bug 868751).

CSS

• The blink effect for text-decoration: blink; has no more effect, but is still a valid value (bug 857820).
• In-flow ::after and ::before pseudo-elements are now flex items (bug 867454).

MathML

• Negative widths for the <mspace> element has been implemented (bug 717546).
• The <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
• Site Compatibility for Firefox 23

Older versions