Firefox 63 for developers

This article provides information about the changes in Firefox 63 that will affect developers. Firefox 63 was released on October 23, 2018.

• The Fonts tab in the Page Inspector now includes an editor that makes it easy to view and edit the settings of the fonts on your page. See Edit fonts for details.
• The Accessibility inspector is now enabled by default (bug 1482454).
• When you hover over an object in the Accessibility Inspector, the item is highlighted and its role and name will be shown in an information bar on the page (bug 1473030).
• The command line in the Web Console is now shown immediately following the console output (bug 1136299).
• A new icon has been added to the content in the Network Monitor to indicate when a URL belongs to a known tracker — see Security icons in [Page not yet written] (bug 1333994).
• The default value of devtools.aboutdebugging.showSystemAddons is now false, meaning that system add-ons will not be listed on the about:debugging page. You can change the settings by navigating to about:config (bug 1425347).
• The Responsive Design Mode toolbar was simplified, and we added the option to left-align the viewport.
• The Page Inspector includes a link to the class definition for a custom element. (bug 1443923).

• Support for the <img> element's decoding attribute has been added (bug 1416328); see also HTMLImageElement.decoding.

Removals

• Support for the sidebar link type (rel="sidebar") has been removed. If an anchor tag includes this attribute, it will be ignored (bug 1452645).

• Support for the :defined pseudo-class has been added (bug 1331334).
• Support for row-gap, column-gap and gap have been added in Flexbox layout (bug 1398483).
• Re-enabled support for webkit-prefixed pixel-density @media queries (bug 1444139).
• Support added for the CSS Flexible Box Layout (Flexbox) properties align-self, align-content, and align-items as well as the justify-content property (bug 1472843).
• Implemented the path() function for offset-path (bug 1429298).
• Implemented syntax improvements from the Media Queries Level 4 specification (bug 1472843).
• Renamed offset-* properties to inset-block-start, inset-block-end, inset-inline-start, and inset-inline-end (bug 1464782).
• Added support for the prefers-reduced-motion media feature (bug 1365045, bug 1475462).
• Added flow relative values (block, inline) for the resize property (bug 1464786).
• Implemented flexbox layout for safe & unsafe values in align-self, align-content, and justify-content (bug 1297774).
• The logical properties (where appropriate) are now animatable (bug 1309752).

Removals

• Removed offset-block-start, offset-block-end, offset-inline-start, and offset-inline-end; these have been renamed to inset-*, as described above (bug 1464782).

No changes.

• The Symbol.prototype.description property has been implemented (bug 1472170).
• The Object.fromEntries() method has been added (bug 1469019).
• When you try to access a property of an undefined object, the error message is now much improved. Considering the case where x is undefined and you try to access x.y, instead of TypeError: x is undefined the console now returns the more descriptive x is undefined; can't access its "y" property (bug 1259822).

Removals

• Experimental WebAssembly Module IndexedDB serialization support has been removed (bug 1469395).

New APIs

• The Shadow DOM (bug 1471947) and Custom Elements (bug 1471948) APIs have been enabled by default; See Web components for more details.
• The Media Capabilities API has been implemented (bug 1409664).
• The Async Clipboard API has been implemented and enabled by default for all channels (bug 1461465). As is the case with Chrome, Firefox currently implements only the writeText() and readText() methods; however, unlike Chrome, readText() is only available in browser extensions.
• The SecurityPolicyViolationEvent interface is now supported. It allows sending events when the Content-Security-Policy is violated (bug 1472661).

DOM

• The following portions of the Web Animations API have been enabled by default (see bug 1476158):
  • The Animation properties ready and finished, specifying the Animation object's ready and finished Promises.
  • The Animation object's effect property.
  • The interfaces KeyframeEffect and AnimationEffect.
• The Element.toggleAttribute() method has been implemented (bug 1469592).
• The historical, previously non-standard, Event.returnValue property is now supported for compatibility purposes (bug 1452569).
• We implemented the Window.event property to improve web compatibility, now that it's become standard (bug 218415). However, due to some web compat issues (e.g. bug 1479964), this was quickly disabled in non-Nightly channels, hidden behind the dom.window.event.enabled pref (bug 1493869).
• To bring Firefox into alignment with Edge and Chrome, the navigator.platform property now returns "Win32" even when running on 64-bit Windows (bug 1472618).
• Prior to Firefox 63, links that open new windows that had rel="noopener", as well as calls to Window.open() with the noopener window feature enabled would default to having all window features disabled so that you had to explicitly re-enable any standard features you wanted. Now, these windows have the same set of features enabled like any other window, and you need to explicitly turn off any you don't want (bug 1419960).

DOM events

• Handling of the Alt key on the right side of the keyboard has been improved on Windows. If the user's current keyboard layout maps the Alt key to the AltGr modifier key, the value of KeyboardEvent.key is now reported as "AltGraph". This behavior matches the behavior recently introduced in Chrome (bug 900750).

Media, Web Audio, and WebRTC

• Microphone access now works simultaneously in multiple tabs, even within the same content process (bug 1404977).
• RTCDataChannel has been updated to support the sctp-sdp-21 data format for the data, in addition to the older sctp-sdp-05 format previously supported.
• The ConstantSourceNode node type for Web Audio API now has a default channel count of 2 rather than 1, in order to match the specification (bug 1413283).
• The Web Audio API interface AudioScheduledSourceNode (and by extension, all the other node types based on it) now throw the correct exception when a negative value is specified for the node start time. That error is RangeError (bug 1413284).
• The minimum and maximum permitted values for an AudioParam object's value have been changed to the minimum negative single-precision floating-point value (-340,282,346,638,528,859,811,704,183,484,516,925,440) and the maximum positive single-precision floating-point value (+340,282,346,638,528,859,811,704,183,484,516,925,440) respectively (bug 1476695).
• The SourceBuffer.changeType method, which allows you to change codecs during an active stream, has been enabled by default. This is part of the Media Source Extensions API (bug 1481166).
• The AudioParam.setValueCurveAtTime() method has been updated to correctly accept an array of floating-point values to indicate the parameter's values to change to over time. Previously, it required a Float32Array (bug 1421091).
• AudioParam.setValueCurveAtTime() has also been updated to correctly return a proper TypeError when a non-finite value is found in the values array (bug 1472095).
• In addition, setValueCurveAtTime() has been updated to ensure that, when the parameter finishes following the specified value curve after the duration elapses, the value of the parameter is set to the last value in the list of values to curve through (bug 1308436).
• The RTCRTPStreamStats dictionary has been renamed to RTCRtpStreamStats for consistency with other WebRTC dictionaries and the specification (bug 1480498).
• Support for the RTCRtpStreamStats dictionary's kind property has been added (bug 1481851).
• The RTCRtpStreamStats dictionary's isRemote property is deprecated and will be removed in Firefox 65. A warning is now output to console when this property is accessed. See this blog post on the Advancing WebRTC blog for details (bug 1393306).

Canvas and WebGL

• A new powerPreference context attribute has been added to HTMLCanvasElement.getContext(). On macOS this allows WebGL non-performance-critical applications and applets to request the low-power GPU instead of the high-power GPU in multi-GPU systems (bug 1349799).

Removals

• The obsolete and non-standard Firefox-only methods Window.back() and Window.forward() have been removed. Please use the window.history.back() and window.history.forward() methods instead (bug 1479486).
• The createObjectURL() and revokeObjectURL() methods are no longer available on ServiceWorker instances due to the potential they introduced for memory leaks to occur (bug 1264182).
• Since it was deprecated in the specification anyway, the limited support for Doppler effects on PannerNode has been removed from the Web Audio API. The AudioListener properties dopplerFactor and speedOfSound have been removed, along with the PannerNode method setVelocity() (bug 1148354).

No changes.

• The Clear-Site-Data header is implemented and no longer behind a preference (bug 1470111).

• Site favicons are now subject to Content Security Policy if one is configured for the site (bug 1297156).
• CSP script-src directive's 'report-sample' expression now recognized when generating violation reports. This directive indicates that a short sample of where the violation occurred should be included in the report. Previously, Firefox always included this sample (bug 1473218).
• Firefox now uses NSS 3.39 (bug 1470914).

No changes.

New features

• Marionette now returns a setWindowRect capability in the WebDriver:NewSession response that is true if the browser window can be repositioned and resized, which e.g. is the case for Firefox but not any mobile applications (bug 1470659).
• Added support for the unhandledPromptBehavior capability, which allows to define a specific prompt behavior of the WebDriver specification (bug 1264259).
• Handling of user prompts has been added to the WebDriver:ExecuteScript and WebDriver:ExecuteAsyncScript commands (bug 1439995).

API changes

• Deprecated command end-points without the WebDriver: prefix have been removed (bug 1451725).
• The WebDriver:NewSession command returns recommended strings (linux, mac, windows) for platformName as defined in the WebDriver specification (bug 1470646).

Bug fixes

• Focus related events were missing on element interaction when Firefox was not running as the top-most application (bug 1398111).
• Performing a pointerDown and pointerUp action in a subsequent action sequence could trigger a double click because WebDriver:ReleaseActions didn't reset the double click tracker (bug 1422583).
• Executing pause actions repeatedly could cause an infinite hang (bug 1447449).
• Fixed a bug where returning an element collection from WebDriver:ExecuteScript and WebDriver:ExecuteAsyncScript would cause a cyclic reference error (bug 1447977).
• To prevent a race condition both the WebDriver:AcceptAlert and WebDriver:DismissAlert commands now wait until the user prompt has been closed (bug 1479368).
• Log entries as emitted by the frame script were no longer limited by MarionettePrefs.logLevel but logged everything (bug 1482829).
• WebDriver:TakeScreenshot raised an error when taking a screenshot of a window larger than 32767 pixels in width or height (bug 1485730).
• WebDriver:SendAlertText didn't replace default user prompt value if text to send is an empty string (bug 1486485).

• Corrected the behavior of PerformanceObserver.observe() to do nothing if no valid entry types are found in the specified array of entry types to observe, or if the array is empty or missing. Previously, Firefox was incorrectly throwing a TypeError (bug 1403027).
• In OpenSearch, Firefox now accepts application/json as a search URL type, as an alias of application/x-suggestions+json (bug 1425827).

Theming

• The default text color for browserAction badges is now automatically set to black or white, to maximize contrast with the background (bug 1474110).
• The accentcolor and textcolor properties of the theme manifest key are now optional (bug 1413144).
• browserAction.getBadgeTextColor() and browserAction.setBadgeTextColor() enable you to get and set the text color of browser action badges (bug 1424620).
• The theme colors key in manifest.json now supports the ntp_text property to set the text color in a new tab, and the ntp_background property to set the color of a new tab (bug 1347204).
• Themes can now define the colors for sidebars, such as the bookmarks sidebar (bug 1418602). The relevant properties include:
  • sidebar: The background color for sidebars.
  • sidebar_text: The text color for sidebars.
  • sidebar_highlight: The background color of a selected item in a sidebar.
  • sidebar_highlight_text: The text color of a selected item in a sidebar.
• The method management.install() allows web extensions to install and enable signed browser themes (bug 1369209).
• The manifest key theme_experiment was introduced (bug 1472740). This key enables the definition of experimental theme key properties for the Firefox interface.

Search

• The new search API enables you to retrieve the list of installed search engines and perform searches with them (bug 1352598).
• topSites.get() now takes an options parameter enabling you to set various options for the list of sites returned (bug 1445836).

Tabs

• tabs.onHighlighted now supports multi-select (bug 1474440).
• tabs.highlight now includes an optional field in the highlightInfo object — populate — which defaults to true. Setting it to false prevents the returned windows.Window object from being populated with a list of tabs, to improve performance (bug 1489814).
• tabs.update now supports changing the selection status of a tab by including highlighted: true in the updateProperties parameter (bug 1479129).
• tabs.update now supports changing the selection status of a tab without changing the focused tab (bug 1486050) by including both highlighted: true and active: false in the updateProperties parameter.
• tabs.query now returns an array of tabs.Tab objects if multiple tabs are selected (bug 1465170).
• The tabs.Tab property now properly reflects which tabs in a browser window are selected (highlighted) and tabs.highlight supports changing the highlighted status of multiple tabs (bug 1464862).
• The isarticle property in the extraParameters object passed into tabs.onUpdated has been renamed to isArticle. The old name is retained but deprecated. This change was uplifted to Firefox 62 (bug 1461695).
• The tabs.onUpdated event can be used to track when a tab is drawing the user's attention with attention property of the changeInfo object (bug 1396684).

Menus

• Added menus.getTargetElement() to the menus API. The method returns the element referenced by the targetElementId parameter that identifies the clicked element. If the targetElementId is no longer valid, the method returns null (bug 1325814).
• menus.create() now enables you to create invisible menu items, and menus.update() enables you to toggle menu item visibility (bug 1482529).
• Items created using the menus API now support access keys (bug 1320462).
• The targetUrlPatterns parameter of menus.create() and menus.update() now supports any URL scheme, even those that are usually not allowed in a match pattern (bug 1280370).
• When a tab context menu item is clicked, the "activeTab" permission is now granted for that tab, even if that's not the currently active tab (bug 1446956).

Other

• commands.onCommand is now treated as user input (bug 1408129).
• The webRequest API now enables you to filter for speculative connections (bug 1479565).
• webRequest.SecurityInfo adds two new properties, keaGroupName, and signatureSchemeName. This change was uplifted to Firefox 62 (bug 1471959).
• cookies.Cookie now includes a property indicating the SameSite state of the cookie. The cookies.SameSiteStatus enumeration defines SameSite state values (bug 1351663).
• Match patterns for URLs now explicitly match the "data" URL scheme (bug 1280370).