Firefox 80 release notes for developers

This article provides information about the changes in Firefox 80 that will affect developers. Firefox 80 was released on August 25, 2020.

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 {{CSSxRef("appearance", "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.