Firefox 71 for Developers

Console:

• The Console's multi-line mode is now available by default.
• Console configuration options are now combined in a new toolbar settings menu (Firefox bug 1523868).

JavaScript debugger:

• Inline variable preview has been enabled (Firefox bug 1576679).
• Logging on events is now available (Firefox bug 1110276), as is the ability to filter by event type.
• The new debugger paused overlay can now be disabled using the devtools.debugger.features.overlay pref (Firefox bug 1579768).
• We've got new keyboard shortcuts for opening the debugger: Ctrl + Shift + Z on Linux/Windows and Cmd + Opt + Z on macOS (Firefox bug 1583042).
• Pausing on a DOM Mutation Breakpoints now mentions the DOM node that has the breakpoint and, if available, the child node that was added/removed (Firefox bug 1576145).
• Locations in pretty printed sources are now correct after pretty-printing and when jumping to the source from the Inspector's events listener tooltip (Firefox bug 1500222).

Network Monitor:

• The Web sockets inspector is now enabled by default (Firefox bug 1573805).
• You can now do a full-text search of request/response bodies, headers, and cookies.
• You can now enter patterns to block specific URLs from loading.
• The Timings tab now exposes timing data sent in the Server-Timing header (Firefox bug 1403051).

Page Inspector:

• Color swatches are now shown next to CSS variable definitions that have color values (Firefox bug 1456167).
• :visited styles are now shown in the CSS rules view (Firefox bug 713106).

• Added the subgrid value from CSS Grid Level 2 to grid-template-columns and grid-template-rows (Firefox bug 1580894)
• Added support for the column-span property to Multiple-column Layout (Firefox bug 1426010)
• Added support for the path() value of clip-path (Firefox bug 1488530)
• Mapped the height and width HTML attributes on the <img> element to an internal aspect-ratio property (Firefox bug 1585637). See the guide to this feature on MDN.

Removals

• CSS Radial Gradients no longer accept negative radii (Firefox bug 1583736).

• The Promise.allSettled() method is now supported (Firefox bug 1549176). This method lets you easily wait until every promise in a set of promises is either fulfilled or rejected before running further code.

Removals

• The non-standard Array generic methods have been removed in Firefox 71 (Firefox bug 1222547). They were first introduced in Firefox 1.5 and deprecated from Firefox 68 onwards. If your use case is to use array generics on array-like objects, you can convert your object to a proper array using Array.from() and then use standard array methods.

• MathML elements now implement a MathML DOM and their class is MathMLElement. With a proper MathML DOM, you can now use mathmlEl.style, or global event handlers, for example. Prior to this change, MathML elements only implemented the Element class (Firefox bug 1571487).

New APIs

The Media Session API is now partially implemented. This API provides a standard mechanism for your content to share with the underlying operating system information about the state of media it's playing. This includes metadata such as artist, album, and track name, as well as potentially album artwork (Firefox bug 1580602).

The API also provides a way to receive notifications when the device's media controls (such as play, pause, and seek buttons) are activated by the user. To that end, the MediaSession interface is now partially implemented, with support for setting and fetching the currently-playing media's metadata and for the setActionHandler() method. To access the MediaSession API, use the navigator.mediaSession property.

DOM

• The StaticRange() constructor is now supported (Firefox bug 1575980).
• The MathML MathMLElement interface has been implemented (Firefox bug 1571487).

Media, Web Audio, and WebRTC

• The MediaRecorder interface now implements the audioBitsPerSecond and videoBitsPerSecond properties (Firefox bug 1514158).

Canvas and WebGL

• The OVR_multiview2 and OES_fbo_render_mipmap WebGL extensions are now exposed by default (Firefox bug 1584277, Firefox bug 1583878).

Removals

The following non-standard DataTransfer members have been removed (Firefox bug 1345192):

• DataTransfer.mozItemCount
• DataTransfer.mozClearDataAt()
• DataTransfer.mozGetDataAt()
• DataTransfer.mozSetDataAt()
• DataTransfer.mozTypesAt()

• Both the WebDriver:TakeScreenshot and WebDriver:TakeElementScreenshot commands have been updated to respect the unhandled prompt behavior setting (Firefox bug 1584927).
• The command Marionette:Quit has been updated to also allow quitting or restarting of other Gecko-driven applications besides Firefox (Firefox bug 1298921).
• For GeckoView-based browsers on Android, the returned browserName in the session capabilities will now always be firefox (Firefox bug 1587364).

• downloads.download now identifies and reports as errors the following HTTP response codes:
  • 404 returning SERVER_BAD_CONTENT
  • 403 returning SERVER_FORBIDDEN
  • 402 and Proxy 407 returning SERVER_UNAUTHORIZED
  • Anything else above 400 returning SERVER_FAILED (Firefox bug 1576333)
• downloads.download now includes the optional options parameter property allowHttpErrors. When set to true, this boolean flag enables a download to continue after encountering an HTTP error. When set to false, a download is canceled when an HTTP error is encountered. Default value: false. (Firefox bug 1578955)

Removals

• The proxy.register() and proxy.unregister() functions have been removed (Firefox bug 1443259). proxy.onRequest should now be used to handle the proxying of requests.

• Hacks release post: Firefox 71: A year-end arrival