An opaque response should be not only cross-origin but also be request with no_cors request mode. To filter out the request with mode Same_origin, navigate, and cors. This patch reuses the algorithm in InternalRequest/FetchDriver to decide whether a response is an opaque response. https://searchfox.org/mozilla-central/rev/da5d08750e504f3710f7ea051327d9c311c39902/dom/fetch/InternalRequest.cpp#331 https://searchfox.org/mozilla-central/rev/da5d08750e504f3710f7ea051327d9c311c39902/dom/fetch/FetchDriver.cpp#1153,1157 Differential Revision: https://phabricator.services.mozilla.com/D117086