[lukax]

Maybe you have an ad-blocker that just hides the popup but does not restore scrolling (scrolling is usually prevented when popups are visible)

[osigurdson]

Firefox has a lot of weird little pop up ads these days. It seems like this is a very recent phenominon. Is this actually Firefox doing this or some kind of plug-in accidentally installed?

[duttish]

Hm, I haven't seen that. Perhaps it's worth reviewing your plugins

[osigurdson]

Thanks! I think it might have been notifications from futurism.com. I don't remember visiting that site or allowing notifications (on purpose anyway).