Firefox 79 for developers
This article provides information about the changes in Firefox 79 that will affect developers. Firefox 79 was released on July 28, 2020.
See also Firefox 79: The safe return of shared memory, new tooling, and platform updates on Mozilla hacks.
Changes for web developers
Developer Tools
Console
- Network messages with response codes in the 400-499 and 500-599 ranges are now considered errors, and are displayed even if Response or XHR filters are disabled. (Firefox bug 1635460)
- Network messages for requests that are blocked (by the browser or an extension) are now styled with a "prohibited" icon in the Console. (Firefox bug 1629875)
Debugger
- "Blackbox" a source file is now called "ignore" a source file. (Firefox bug 1642811)
- Inline preview is now available on exceptions. (Firefox bug 1581708)
- Items in the Watch Expressions and Scopes sections now have tooltips on hover, showing their values (Firefox bug 1631545)
- In the Call Stack section, there is now a context menu option to Restart Frame, to execute the current stack frame from its beginning. (Firefox bug 1594467)
Other tools
- The new Application panel is now available, which initially provides inspection and debugging support for service workers and web app manifests.
- The Messages tab of the Network Monitor has been merged with the Responses tab. (Firefox bug 1636421)
- The Accessibility Inspector is automatically turned on when you access its tab; you no longer need to explicitly enable it. (Firefox bug 1602075)
- In Responsive Design Mode, when touch simulation is enabled, mouse-drag events are now interpreted as touch-drag or swipe events. (Firefox bug 1621781)
- When remote debugging, the URL bar now has Back and Forward buttons to help with navigation on the remote browser. (Firefox bug 1639425)
HTML
- The
<iframe>
element'ssandbox
attribute now supports theallow-top-navigation-by-user-activation
token (Firefox bug 1359867). - Setting
target="_blank"
on<a>
and<area>
elements implicitly provides the same behavior as also settingrel="noopener"
(Firefox bug 1522083).
CSS
- External style sheets are now cached per document group (Firefox bug 1599160). Firefox will minimize retrieval and revalidation of cached style sheets when navigating pages on the same origin. A simple reload (for example,
F5
) will not revalidate the cached CSS files. To load current versions of the style sheets, reload the page bypassing the cache (Cmd
/Ctrl
+F5
).
Removals
- The
prefers-color-scheme
media feature'sno-preference
value has been removed from the media queries spec, and from Firefox (Firefox bug 1643656).
JavaScript
SharedArrayBuffer
has been re-enabled in a post-Spectre-safe manner. It is available to cross-origin isolated sites (Firefox bug 1619649).- To cross-origin isolate your site, you need to set the new
Cross-Origin-Embedder-Policy
(COEP) andCross-Origin-Opener-Policy
(COOP) headers.
- To cross-origin isolate your site, you need to set the new
Promise.any()
is now available (Firefox bug 1599769).WeakRef
objects have been implemented (Firefox bug 1639246).- Logical assignment operators are now supported (Firefox bug 1639591)
Atomics
objects now also work with non-shared memory (Firefox bug 1630706).- The
Intl.DateTimeFormat()
constructor now supports thedateStyle
andtimeStyle
options (Firefox bug 1557718). - The
Intl.NumberFormat()
constructor now supports more numbering systems (Firefox bug 1413504).
HTTP
- Cross-origin isolation has been implemented using the new
Cross-Origin-Embedder-Policy
(COEP) andCross-Origin-Opener-Policy
(COOP) headers. This allows you to access certain features such asSharedArrayBuffer
objects and unthrottled timers inPerformance.now()
.
APIs
DOM
- The
FileReader
interface'sloadstart
event is now dispatched asynchronously, as per the spec (Firefox bug 1502403). CanvasPattern.setTransform()
now supports aDOMMatrix
object as an input parameter, as well as anSVGMatrix
object (Firefox bug 1565997).
Media, WebRTC, and Web Audio
- Firefox now supports remote timestamps on statistics records whose
RTCStats.type
isremote-outbound-rtp
. TheRTCRemoteOutboundRtpStreamStats
dictionary which is used to provide these statistics now includes theremoteTimestamp
property, which states the timestamp on the remote peer at which the statistics were collected or generated (Firefox bug 1615191).
Removals
- A number of internal Gecko events — including
DOMWindowClose
— which were accidentally exposed to the web, are now internal-only as intended (Firefox bug 1557407).
WebAssembly
- WebAssembly Bulk memory operations are now shipped (Firefox bug 1528294).
- WebAssembly Reference types are now shipped (Firefox bug 1637884).
- WebAssembly Threads (Shared memory & Atomics) are now shipped (Firefox bug 1389458, Firefox bug 1648685).
Changes for add-on developers
Older versions
- Firefox 78 for developers
- Firefox 77 for developers
- Firefox 76 for developers
- Firefox 75 for developers
- Firefox 74 for developers
- Firefox 73 for developers
- Firefox 72 for developers
- Firefox 71 for developers
- Firefox 70 for developers
- Firefox 69 for developers
- Firefox 68 for developers
- Firefox 67 for developers
- Firefox 66 for developers
- Firefox 65 for developers
- Firefox 64 for developers
- Firefox 63 for developers
- Firefox 62 for developers
- Firefox 61 for developers
- Firefox 60 for developers
- Firefox 59 for developers
- Firefox 58 for developers
- Firefox 57 for developers
- Firefox 56 for developers
- Firefox 55 for developers
- Firefox 54 for developers
- Firefox 53 for developers
- Firefox 52 for developers
- Firefox 51 for developers
- Firefox 50 for developers
- Firefox 49 for developers
- Firefox 48 for developers