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 will be the 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).



Media, WebRTC, and Web Audio

  • The Media Session API now supports the seekto action, allowing media controls to request that your code seek to a specific time offset within the media you're playing (bug 1621403).
  • The Media Session API also now supports the skipad action, which skips past the current advertising or promotional content to continue playing the main media content, if the capability exists and if the user's subscription or permissions level allows ad skipping (bug 1582569).




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

WebDriver conformance (Marionette)

  • Using WebDriver:NewWindow to open a new tab returned too early when running tests in headless mode (bug 1653281).
  • Removed name argument for WebDriver:SwitchToWindow, which is not supported for W3C-compatible mode, and shouldn't be used anymore (bug 1588424).
  • 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 by an arbitrary script that calls, will automatically switch to that new window (bug 1661495).

Changes for add-on developers

No changes


See also

Older versions