Thanks... The fact that websites are now blocking Firefox by default as an "ad-blocker" is saddening.
I opened a firefox private window and navigated to it from the HN page, and got the adblocker popup.
Right now I have two tabs open in the same non-private window, one showing the adblocker popup and one not. In the one that's not I can view the whole page. Reloading in the one that is not showing the adblocker popup then showed it.
I navigated from HN in a non-private window and got the popup. So this seems to be referer constrained in some sense, not necessarily browser based. Hard to confirm.
May be an a-b test?