There isn't any documentation that I can find on what "NS_ERROR_DOM_COOP_FAILED" means, but it seems like it was a transient glitch.
745 # Used to indicate that a resource load was blocked because of the
746 # Cross-Origin-Opener-Policy response header.
747 # https://html.spec.whatwg.org/multipage/origin.html#cross-origin-opener-policies
748 errors["NS_ERROR_DOM_COOP_FAILED"] = FAILURE(1041)
Most interestingly, Firefox source code seems to indexed by a handful of SEO-infested source code indexing sites, but not by the major search engines, at least not with enough relevance. 🤔
@th coop failed? the chickens will escape!!