Firefox 82 for developers

• You can now inspect server-sent events using the Network Monitor (Firefox bug 1640857).
• The Network Monitor's Message panel has now been merged with the Response panel — messages (e.g. from WebSockets or server-sent events) can now be viewed right below the responses list (Firefox bug 1636421).

• The color picker used for <input type="color"> is now keyboard-accessible on Windows (Firefox bug 1526820).
• The allow-downloads flag for the <iframe sandbox> attribute is now supported (Firefox bug 1656212).

• Support for the new ::file-selector-button pseudo-element has been added. This pseudo-element represents the file selection button inside an <input type="file"> element (Firefox bug 1635675, Firefox bug 1662478).
• We have improved error recovery for the :is() and :where() pseudo-classes. These pseudo-classes now accept a forgiving selector list, where an invalid selector in the list will not render the entire list invalid (Firefox bug 1664718).
• appearance: button now applies only to buttons; the button value of appearance will otherwise behave as auto (Firefox bug 1662703).

Removals

• We have removed the proprietary :-moz-user-disabled pseudo-class (Firefox bug 1664432).

• 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

• The Media Session API is now enabled by default (Firefox bug 1665496).

DOM

• 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 window.name 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 window.name for cross-domain messaging (Firefox bug 444222).

• 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).

• 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).