When showPopover or hidePopover are called on elements and they are already in the requested state, these methods should not throw. When showModal or show are called on dialog elements and they are already in the requested state, these methods should not throw. HTML spec PR: https://github.com/whatwg/html/issues/9045 WPT: https://github.com/web-platform-tests/wpt/pull/39781
*** This bug has been marked as a duplicate of bug 255879 ***