I actually just wrote a blog post about this topic: https://videoinu.com/blog/firefox-reader-view-heuristics https://videoinu.com/blog/firefox-reader-view-heuri

I actually just wrote a blog post about this topic: https://videoinu.com/blog/firefox-reader-view-heuristics https://videoinu.com/blog/firefox-reader-view-heuristics In a nutshell, the paragraphs (<p> tags) do not contain enough text to contribute to the readability score. Reader view heuristics rewards paragraphs of at least 140 characters.