Firefox 80 for developers

• You can now block and unblock network requests using the :block and :unblock helper commands in the Web Console (bug 1546394).
• When adding a class to an element in the Page Inspector's Rules pane, existing classes are suggested with autocomplete (Refer to 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 (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 (bug 1648373).

No changes.

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

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

• 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 (bug 1608358).

DOM

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

Removals

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

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

• Using WebDriver:NewWindow to open a new tab no longer returns too early when running tests in headless mode (bug 1653281).
• We removed the name argument for WebDriver:SwitchToWindow — it is not supported for W3C-compatible mode, and shouldn't be used anymore (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 (bug 1661495).

No changes.