Site Compatibility for Firefox 19


Firefox 19 Beta was released on . While it has been developed to maintain compatibility as much as possible, the new version includes some changes affecting backward compatibility aimed at improving interoperability with the other browsers or following the latest Web standards. Here's the list of such changes — Hope this helps whenever you test your sites or applications.

This article only explains the changes that may affect backward compatibility for Websites. For the other new features and changes, please read the following documents:

This list may be updated until the release of the final version, so please check back later.



The CSS3 flexible boxes (flexbox) implementation has been prefixed. From now on, use the related properties and keywords without moz prefix. Note that the flexbox is still disabled by default in Firefox 19. If you'd like to test the feature, open about:config and change the value of layout.css.flexbox.enabled to true.


The -moz-initial keyword has been unprefixed. While -moz-initial will remain in the meantime as an alias of initial, it will be removed at some time, so use the unprefixed keyword instead.


The :-moz-placeholder pseudo-class that matches form elements with the placeholder attribute has been removed, and the ::-moz-placeholder pseudo-element has been added instead. The implementation of WebKit has been a pseudo-element, and this change is a part of the standardization effort.


Following the latest CSS3 animations spec, key frame rule declarations with the !important keyword are now be ignored and parse errors will be returned.


While this is not a change affecting site compatibility, it's worth mentioning because this has been developed as part of efforts to keep compatibility. Preferences to disable some major prefixed properties have been added: layout.css.prefixes.border-image, layout.css.prefixes.transforms, layout.css.prefixes.transitions and layout.css.prefixes.animations. Web developers can disable those preferences (change the values to false) to test whether style rules are applied as intended even after those prefixed implementations are removed.


Element.getElementsBy* 现在将返回HTMLCollection对象

getElementsByTagName, getElementsByTagNameNS以及getElementsByClassName方法返回的元素列表对象的类型从NodeList(遵循DOM3核心规范)变为HTMLCollection(遵循DOM4规范草案).


The document.implementation.hasFeature and Element.isSupported methods have been changed to always return true. The spec has been changed because those APIs were considered useless. However the SVG features are exception; those methods continue to return the support statuses.


Previously the document.createElement method has thrown exception INVALID_CHARACTER_ERR if the argument was null. The method now returns the HTMLUnknownElement object because the argument should be treated as a string and considered to be the same code as document.createElement("null").


When the URL of a nested inline frame (iframe) or a grandchild window is programmatically changed from the parent window, the value of the document.referrer property now points the URL of the parent window where the script is written instead of the child window that refers directly. This is due to a change of the spec and leads to the same behavior as Internet Explorer and Opera. WebKit to follow.


Following the latest File API spec, the lastModifiedDate property of a File object now returns the current date if the file's last modified date is unknown. Previously it returns null in such case.

Encoding API 遵循了最新规范

Following a change of the Encoding API spec, the implementation of TextEncoder and TextDecoder has been updated.


The XML Events implementation has been removed. The development of the Mozilla XForms extension that has used the API has been practically discontinued. The XForms accessibility support has also been removed from Firefox 19.



The size method, that returns the number of key/value pairs saved in a Map object and the number of values saved in a Set object, are changed to be read-only properties.



Previously, the onbeforeunload attribute has been recognized even if it has been set on any elements, and the named handler is called when the event is fired. To comply with the spec, it's now ignored when it has been set on elements other than body and frameset. The other attributes treated the same include onafterprint, onbeforeprint, onhashchange, onoffline, ononline, onpagehide, onpageshow, onpopstate, onresize and onunload.



The name parameter included in the HTTP Content-Disposition header used for file downloading is now ignored. This parameter is non-standard and supported only by Firefox and Google Chrome. From now, use the standard filename parameter instead.


移除了对Carbon NPAPI的支持

The Carbon event model and the Quickdraw drawing model, deprecated since Firefox 4, are no longer available. Webmasters should make sure your content works well if it requires any special plug-in. If it doesn't work on Firefox 19, please contact the plug-in vendor.


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