> This new trend of content appearing while scrolling down is so terrible accessibility-wise, I do not understand how Mozilla of all institutions would do it.

Could you explain what is wrong with the accessibility of this page? All the content is included in the html payload, so it is accessible to screen readers and text-based browsers; and as for the "reveal" effect, it seems to respect user's choice of "prefers reduced motion" and is disabled when that is user's preference.