title	slug
Firefox 21 for developers	Mozilla/Firefox/Releases/21

Web 开发者需要注意的变化

实现了{{HTMLElement("style")}}元素上的scoped属性。拥有该属性的{{HTMLElement("style")}}元素可以通过在 Firefox 20 中实现的 CSS 伪类{{cssxref(":scope")}}选择器选择到.(Firefox bug 508725).
实现了新的{{HTMLElement("main")}}元素 (Firefox bug 820508).

E4X,一个古老的 JavaScript 扩展 (ECMA-357),已经被删除。因为一直以来，只有 Gecko 支持它.(Firefox bug 788293).
parseInt不再将以"0"开头的字符串作为 8 进制数字来解析 (Firefox bug 786135).

{{cssxref("user-select", "-moz-user-select")}}属性的属性值在设置为 none 时和设置为 -moz-none 时效果等同于，这样才能让 Gecko 和其他内核 WebKit(Chrome, Safari),Presto (Opera) 以及 Trident(Internet Explorer) 中的表现相同 (Firefox bug 816298).
On XHTML content, the auto value of {{cssxref("hyphens", "-moz-hyphens")}} incorrectly applied hyphenation rules when the language was not explicitly declared. This is fixed by (Firefox bug 702121).
CSS 属性{{cssxref("-moz-orient")}}现在支持新的值 auto. 当应用到一个{{HTMLElement("meter")}}元素或者{{HTMLElement("progress")}}元素上时，auto 就等同于 horizontal(Firefox bug 835883).

实现了{{domxref("window.location")}}上的 origin 属性 (Firefox bug 828261).
实现了 <input type="time"> 对象上的 valueAsDate 和 valueAsNumber 方法 (Firefox bug 781570).
实现了 <input type="time"> 对象上的 min 和 max 属性 (Firefox bug 781572).
Some new keyCodes for volume control are supported (Firefox bug 674739).
Some new keyCodes for ancient keyboard layout such as AS/400 are now supported on Windows and Linux (Firefox bug 833719).
Various keyCode values for OEM sepecific keys on Windows are now supported again (Firefox bug 833719).
实现了window.crypto.getRandomValues函数 (Firefox bug 440046)。

更新 CSP 实现到最新的 CSP 规范 1.0(CR):
- Support for the spec-compliant Content-Security-Policy HTTP header (in addition to the experimental X-Content-Security-Policy) has been added (Firefox bug 783049). Note: the patch for this new header landed in Firefox 21, it is disabled on builds (Firefox bug 842657).

附加组件和 Mozilla 开发者需要注意的变化

FUEL applications cannot use the Livemarks service anymore (Firefox bug 834492). The Livemarks service is deprecated and phased out in favor of the new async interface.
History API saw numerous deprecated API being removed:
- Replaced by mozIAsyncFavicons:
  - nsIFaviconService::setFaviconUrlForPage
  - nsIFaviconService::setFaviconData
  - nsIFaviconService::getFaviconData
  - nsIFaviconService::getFaviconForPage
  - nsIFaviconService::setAndLoadFaviconForPage
  - nsIFaviconService::getFaviconImageForPage
  - nsIFaviconService::getFaviconDataAsDataURL
- Replaced by mozIAsyncLivemarks:
  - nsILivemarkService::*
  - PlacesUtils.itemIsLivemark
  - PlacesUtils.nodeIsLivemarkContainer
  - PlacesUtils.nodeIsLivemarkItem
- Removed only third argument:
  - PlacesUIUtils.showBookmarkDialog
- No more implemented by Places, use mozIAsyncHistory instead:
  - nsIGlobalHistory2::addURI
  - nsIGlobalHistory2::isVisited
  - nsIGlobalHistory2::setPageTitle
- No more needed, use onDeleteURI or onItemRemoved:
  - nsINavHistoryObserver::OnBeforeDeleteURI
  - nsINavBookmarkObserver::OnBeforeItemRemoved
- Never implemented properly:
  - nsINavHistoryFullVisitResultNode
- Deprecated, use mozIAsyncHistory::updatePlaces instead:
  - nsINavHistoryService::AddVisit