Firefox 82 for developers

This article provides information about the changes in Firefox 82 that will affect developers. Firefox 82 was released on October 20, 2020.

Note: See also Coming through with Firefox 82 on Mozilla Hacks.

Changes for web developers

Developer tools





  • The Content-Disposition header's inline directive will now be ignored if the HTML <a> element's download attribute is specified (for same-origin URLs). Note that if specified the Content-Disposition header filename will be used in preference to a filename specified in the download attribute (Firefox bug 1658877).


New APIs


  • Document.execCommand() is no longer supported for nested/recursive calls, which will now return false (Firefox bug 1634262).
  • Element.setPointerCapture() throws the NotFoundError exception if the pointer id is invalid, as per the specification (Firefox bug 1662124). Previously it wrongly threw an InvalidPointerId exception.
  • The property is reset to an empty string if a tab loads a page from a different domain, and restored if the original page is reloaded (e.g. via the "back" button). This prevents an untrusted page from accessing any information that the previous page might have stored in the variable. This change may impact frameworks that use for cross-domain messaging (Firefox bug 444222).

WebDriver conformance (Marionette)

  • To simulate a more realistic user navigation, all supported navigation commands have been moved to the parent process (Firefox bug 1612831).
  • We updated the checks for the current or top-level browsing context for all the commands to improve conformance with the WebDriver specification (Firefox bug 1493108).
  • Fixed a bug in WebDriver:ElementClick that sometimes caused the command to return before the click event was actually synthesized (Firefox bug 1394354).

Changes for add-on developers

  • The tabs.captureTab() and tabs.captureVisibleTab() methods now capture an area of the relevant tab's content specified by the rect property of the provided options object, or the visible area of the tab if this property is not provided (Firefox bug 1636508). Previously the rect property was not available, and these methods always captured the visible area of the relevant tab.
  • Read-only access to cookieStoreId no longer requires the "cookies" permission (Firefox bug 1662329).

Older versions