Firefox 80 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


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).





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

WebDriver conformance (Marionette)

  • 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, now automatically switches to that new window (bug 1661495).

Changes for add-on developers

No changes.

Older versions