Firefox 80 release notes for developers

Changes for web developers

Developer Tools

• You can now block and unblock network requests using the :block and :unblock helper commands in the Web Console (Firefox bug 1546394).
• When adding a class to an element in the Page Inspector's Rules pane, existing classes are suggested with autocomplete (Refer to Firefox bug 1492797).
• When the Debugger breaks on an exception, the tooltip in the source pane now shows a disclosure triangle that reveals a stack trace (Firefox bug 1643633).
• In the Network Monitor request list, a turtle icon is shown for "slow" requests that exceed a configurable threshold for the waiting time (Firefox bug 1648373).

HTML

No changes.

CSS

• The standard, unprefixed appearance property is now supported; existing -moz-appearance and -webkit-appearance are now aliases of the unprefixed property (Firefox bug 1620467).

JavaScript

• The ECMAScript 2021 export * as namespace syntax for the export statement is now supported (Firefox bug 1496852).

HTTP

• Previously, when the fullscreen directive was applied to an <iframe> (i.e., via the allow attribute), it didn't work unless the allowfullscreen attribute was also present This has now been fixed (Firefox bug 1608358).

APIs

DOM

• Web Animations API compositing operations are now enabled — see KeyframeEffect.composite and KeyframeEffect.iterationComposite (Firefox bug 1652676).

Removals

• The outerHeight and outerWidth features of Window.open() are no longer exposed to web content (Firefox bug 1623826).

WebAssembly

• Atomic operations are now allowed on non-shared memories (Firefox bug 1619196).

WebDriver conformance (Marionette)

• Using WebDriver:NewWindow to open a new tab no longer returns too early when running tests in headless mode (Firefox bug 1653281).
• We removed the name argument for WebDriver:SwitchToWindow — it is not supported for W3C-compatible mode, and shouldn't be used anymore (Firefox bug 1588424).
• We've started to add Fission support for the following commands: WebDriver:FindElement, WebDriver:FindElements, WebDriver:GetElementAttribute, WebDriver:GetElementProperty.
• Known issue: Opening a new tab by using WebDriver:NewWindow, or via an arbitrary script that calls window.open(), now automatically switches to that new window (Firefox bug 1661495).

Changes for add-on developers

No changes.