FF's built-in reader (keyboard shortcut “F9”) does not display all relevant content

[mrq]

I use this reader a lot and noticed that it does not always display all the text content of the page. It omits some tags in texts e.g. html books. In particular it doesn't display headings and this makes it difficult to understand the content especially using the read aloud function.

[mashdots]

I can confirm this experience as well. Sometimes it omits entire paragraphs for me.