Because Reader Mode is using heuristics to fetch the content of the article, and that can fail if the article is weirdly formatted in HTML. You can read more ab

Because Reader Mode is using heuristics to fetch the content of the article, and that can fail if the article is weirdly formatted in HTML. You can read more about this on the repo for Mozilla's Readability, which is what Firefox uses under the hood: https://github.com/mozilla/readability https://github.com/mozilla/readability