Description
Basically, the problem raised by @bzbarsky in https://esdiscuss.org/topic/figuring-out-the-behavior-of-windowproxy-in-the-face-of-non-configurable-properties two years ago now was resolved, but the resolution could not be implemented per https://bugzilla.mozilla.org/show_bug.cgi?id=1197958#c4 and therefore the HTML Standard's WindowProxy
object definition contradicts ECMAScript here after I discussed the situation with bz and @ajklein.
See https://html.spec.whatwg.org/multipage/browsers.html#windowproxy-getownproperty (step 3) and https://html.spec.whatwg.org/multipage/browsers.html#windowproxy-defineownproperty (also step 3) for the violations.
(I missed this when reporting the document.all violation as this one was not properly tagged in HTML.)