Reader View Omits "Basic Information" and "Quick Answers" on Fandom Pages

Filing on behalf of MarjaE, originally filed at https://bugzilla.mozilla.org/show_bug.cgi?id=2056729.

Steps to reproduce:

Visit https://queercomics.fandom.com/wiki/Constance_Lara_Kent

Visit https://warhammer40k.fandom.com/wiki/Alpharius_Omegon

Can't scroll either page due to non-scrolling background, (anti-)navigation buttons.

Try to view page in Reader View.

Actual results:

Reader View skips "Basic Information" in the former, "Quick Answers" in the latter.

Expected results:

Reader View shouldn't skip "Basic Information" and probably shouldn't skip "Quick Answers".

Firefox should also include better protection against non-scrolling elements, since they're everywhere.