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 (Firefox bug 1620467).



  • 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).





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

Changes for add-on developers

No changes.

Older versions