Firefox 19 for developers

• Map and Set objects have changed from having a size() method to a size property (Firefox bug 807001)
• Map and Set objects also have a clear() method now. (Firefox bug 805003)

• Support for the viewport-relative <length> units, vh, vw, vmin, and vmax, has landed (Firefox bug 503720)
• CSS Flexbox has been unprefixed, but remains disabled by default (Firefox bug 801098).
• The -moz-initial value has been unprefixed (Firefox bug 806068). -moz-initial will be kept for a while as an alias; however, authors are strongly encouraged to switch over to initial.
• The CSS text-transform property now supports the full-width keyword, which allows a more seamless inclusion of Latin characters in text using ideographic fixed-width characters, like Chinese or Japanese (Firefox bug 774560).
• The CSS page-break-inside has been implemented (Firefox bug 685012).
• The CSS calc() function can now be used on <color-stop> (on <gradient>).
• The CSS @page at-rule is now supported (Firefox bug 115199). Note that the pseudo-classes :first, :right, and :left are not yet implemented.
• The :-moz-placeholder pseudo-class is replaced by the ::-moz-placeholder pseudo-element (Firefox bug 737786).
• Declarations qualified with !important appearing in @keyframes are now ignored, per spec (Firefox bug 784466).

• The Element.getElementsByTagName, Element.getElementsByTagNameNS and Element.getElementsByClassName methods now return a live HTMLCollection (Firefox bug 799464).
• The File mozLastModifiedDate property has been implemented. (Firefox bug 793955)
• The File lastModifiedDate property returns the current date, when the date of the last modification is unknown. (Firefox bug 793459
• The CanvasRenderingContext2D isPointInStroke method has been implemented (Firefox bug 803124).
• The HTMLCanvasElement toBlob method has been implemented (Firefox bug 648610).
• The Node.isSupported and the document.implementation.hasFeature() methods have been changed to always return true (Firefox bug 801425).
• When calling document.createElement(null), null will now be stringified and works like document.createElement("null").
• The TextDecoder and TextEncoder interfaces have been updated to match the latest spec (Firefox bug 801487).

Support for XForms has been removed in Firefox 19.

• getBrowserSelection() now returns the selected text in a text input field. As a result, gContextMenu.isTextSelected will be true when the user selects text in a text input field that is not a password field. (Firefox bug 565717)
• Dict.jsm: Dict() now takes a JSON String. Dict.toJSON() was added, and it returns a JSON String. (Firefox bug 727967)

nsIImgLoadingContent

The parameter (aObserver) of addObserver() method changes from imgIDecoderObserver to imgINotificationObserver. The notify() method of imgINotificationObserver is not scriptable, so you need to use createScriptedObserver() from imgITools.

nsIChannel

The property contentLength changed from long to int64_t.

• Firefox 19 Beta Release Notes
• Add-on Compatibility for Firefox 19