A nag popup where the dismiss button just changes itself instead of dismissing the window? Oof, that's a new one.

The Kill Sticky bookmarklet is your friend: https://alisdair.mcdiarmid.org/kill-sticky-headers/

There's a newer version, but it breaks a number of sites for me, so I don't use it: https://github.com/t-mart/kill-sticky

The internet is a hostile place without Kill Sticky, uBlock Origin, and uBlock Matrix.