In your agenda to expose my agenda in linking a Firefox blog post, you have missed that this isn't even about captive portal detection. Captive portals are easily detected by trying to load a known response page; captive portals don't fake that because they want to be detected so that the browser redirects you to their portal.

This is about malicious DNS resolvers that don't return NXDOMAIN for non-existent domains but instead send you to an ISP advertisement page. This messes with the omnibox. For all other domains, they resolve just fine. These resolvers are inclined to evade detection, e.g. if browsers checked a static list of domains, they would just return NXDOMAIN for only those.