So it seems Stuff are blocking ad blockers now, yay. I can block the overlay with uBlock but the page doesn't scroll which is sometimes an issue.
But TIL they are using a third party site for the quizzes, and you can pop out the embedded iFrame, change one parameter in the URL so it doesn't fill the whole page, and then it's much more pleasant on a distraction free page and no stuff header bar filling 1/3 of the page.