I don't think this is new, is it? For at least the last couple of years (maybe longer, that's just how long I've used Firefox on Windows) some sites are hardcoded not to allow extensions to run on them. As an example, add-ons don't run on addons.mozilla.org for security purposes. Is there any reason to think this is a conspiracy about ad blockers? I haven't seen anything that indicates this isn't the same as the addons.mozilla.org situation.