Firefox 70 for developers

This article provides information about the changes in Firefox 70 that will affect developers. Firefox 70 was released on October 22, 2019.

Changes for web developers

Developer tools

Debugger updates

• In the Debugger you can now set breakpoints forDOM Mutation, so execution will pause when a node or its attibutes are changed or when a node is removed from the DOM (bug 1576219).
• The Debugger now shows an overlay on the page when it is paused, with basic stepping buttons to let you step and continue (bug 1574646).
• The Debugger now shows sources that already got discarded by the engine (usually scripts that execute once during page load), so you can properly set breakpoints to debug when they execute next (bug 1572280).
• The Debugger'sscopes panel grouping has been simplified, consolidating additional scopes previously shown above the top level function (e.g. blocks created by let , with , or if / else ) (bug 1448166)
• The Debugger now retains the currently selected and expanded variables in thescopes panel while stepping (bug 1405402).
• The Debugger now handles stepping over async functions correctly, making asynchronous function debugging easier (bug 1570178).
• When debugging inContainer sessions (useful for testing different logins), the sources in the debugger are now shown correctly (bug 1375036).
• debugger statements can be now disabled in the Debugger by setting a breakpoint on them and switching the breakpoints to "Never pause here" (bug 925269).

Other updates

• An icon will be displayed next to inactive CSS properties in theRules view of thePage Inspector, which you can hover over to get information on why it is inactive (bug 1306054).
• In theCSS Rules view, thecolor picker on foreground colors now tells you whether its contrast with the background color meets accessibility conformance criteria (bug 1478156).
• The Accessibility inspector 'sCheck for issues dropdown now includes keyboard accessibility checks (bug 1564968).

HTML

• Firefox can now suggest securely-generated passwords to the user in the following situations:
  • An <input> element has the autocomplete="new-password" attribute value.
  • The user opens the context menu on any password input element, even if it is not intended for new passwords.

CSS

• Opacity values like for opacity or stop-opacity can now be percentages (bug 1562086).
• grid-auto-columns and grid-auto-rows now accept multiple track-size values (bug 1339672).
• A number of text-related CSS properties have been enabled by default (bug 1573631):
  • text-decoration-thickness .
  • text-underline-offset .
  • text-decoration-skip-ink . The default value is auto , which means that by default underlines and overlines are now interrupted where they would otherwise cross over aglyph.
• The display property now accepts two keyword values representing the inner and outer display type (bug 1038294,bug 1105868 and bug 1557825).
• The font-size property now accepts the new keyword value xxx-large . (bug 1553545).
• The :visited pseudo-class no longer matches <link> elements, for logic and performance reasons (bug 1572246; see Intent to ship: Make <link> elements always unvisited and [selectors] :link and <link> for more reasoning as to why).
• We now support an auto value for the quotes property (bug 1421938).
• Stylesheets contained in <style> elements are now cached for reuse, to improve performance (bug 1480146). Note that this currently doesn't include stylesheets that contain @import rules.
• The <ratio>  type now accepts <number>/<number> or a single <number> as a value. (bug 1565562).

Removals

• We have retired support for 3-valued <position> (excluding background)(bug 1559276). See site compat note .
• The none value is now invalid in counter()  /  counters() — a change which makes the Level 3 spec match CSS 2.1bug 1576821).

SVG

• Cut, copy, and paste events are now dispatched to SVG graphics elements (bug 1569474).

JavaScript

• Numeric separators are now supported (bug 1435818).
• The Intl.RelativeTimeFormat.formatToParts() method has been implemented (bug 1473229).
• The BigInt.prototype.toLocaleString() method has been updated to work with the locales and options parameters per the ECMAScript 402 Intl API. Also, Intl.NumberFormat.format() and Intl.NumberFormat.formatToParts() now accept BigInt values (bug 1543677).
• Per the latest ECMAScript specification, a leading zero is now never allowed forBigInt literals, making 08n and 09n invalid similar to the existing error when legacy octal numbers like 07n are used. Always use a leading zero with the letter "o" (lowercase or uppercase) for octal BigInt numbers (i.e. 0o755n instead of 0755n ). Seebug 1568619.
• The Unicode extension key "nu" is now supported for the Intl.RelativeTimeFormat constructor and the Intl.RelativeTimeFormat.resolvedOptions() method now also returns numberingSystem ( bug 1521819 ).

APIs

DOM

• The back() , forward() , and go() methods are now asynchronous. Add a listener to the popstate event to get notification that navigation has completedbug 1563587.
• We've added support DOMMatrix , DOMPoint , etc. in web workers (bug 1420580).
• A few more members have been moved from HTMLDocument to Document , including  Document.all , Document.clear , Document.captureEvents , and Document.clearEvents ( bug 1558570 , bug 1558571 ).

Workers/Service workers

• Strict MIME type checks are now enforced on worker and shared worker scripts, i.e. those targetted by the Worker() and  SharedWorker() constructors (bug 1523706).

Media, Web Audio, and WebRTC

• The RTCPeerConnection.restartIce() method has been added. This is one of the four changes needed to implement the new "perfect negotiation" mechanism; the rest will come in future Firefox updates (bug 1551316).
• The RTCPeerConnection.setRemoteDescription() method can now be called with no parameters. This is another "perfect negotiation" update (bug 1568292).
• MediaTrackSupportedConstraints.groupId is now supported, and returns  true since the MediaTrackConstraints.groupId property is now supported (bug 1561254).
• Several new Web Audio API features have been implemented/updated:
  • AudioContext.getOutputTimestamp() implemented (bug 1324545).
  • AudioContext.baseLatency and  AudioContext.outputLatency implemented (bug 1324552).
  • MediaElementAudioSourceNode.mediaElement and MediaStreamAudioSourceNode.mediaStream implemented (bug 1350973).
  • The ChannelMergerNode() constructor now throws errors if you try to set channelCount and channelCountMode to invalid values (bug 1456263).

Canvas and WebGL

• We now support CanvasRenderingContext2D.getTransform() , and the newer variant of CanvasRenderingContext2D.setTransform() that accepts a matrix object as a parameter rather than multiple parameters representing the individual components of the matrix (bug 928150).

HTTP

• The default referrer policy for third-party tracking resources is now strict-origin-when-cross-origin when Enhanced Tracking Protection is turned on (bug 1569996).
• The size of the Referer request header is now limited to 4 KB (4,096 bytes). If an overly long referer exceeds the defined limit, only the origin part will be sent (bug 1557346).
• TheHTTP cache is now partitioned per the top-level document's origin (bug 1536058).

Removals

• The X-Frame-Options allow-from uri directive has been removed. Use the Content-Security-Policy header with the frame-ancestors directive instead (bug 1301529).

WebDriver conformance (Marionette)

• Updated the WebDriver:TakeScreenshot command to beFission compatible. It means that content fromcross-origin iframes is now included in a page's screenshot. Or when using it from chrome scope that the active tab's content is visible now inside the browser window. (bug 1559592).
• WebDriver:TakeScreenshot no longer accepts a list of DOM elements as used for highlighting (bug 1575511).
• WebDriver:ExecuteScript and WebDriver:ExecuteAsyncScript no longer sets window.onunload in ways that are web-exposed (bug 1568991).

Changes for add-on developers

API changes

• Added a new parameter to the topSites.get() method that causes the method to return the list of pages that appear when the user opens a new tab (bug 1568617).
• The privacy.network property's WebRTCIPHandlingPolicy sub-property's permitted values have been amended (inbug 1452713) to match the behavior seen in Chrome as follows:

  disable_non_proxied_udp
  proxy_only
  

Manifest changes

Removals

The followingtheme key properties, which provided aliases for theme keys used in chromium-based browsers, were removed:

• images property headerURL , themes should now use theme_frame .
• colors properties:
  • accentcolor , themes should now use frame .
  • textcolor , themes should now use tab_background_text .