How Firefox Reader View Works to Clean Up Web Pages

Firefox’s Reader View transforms cluttered web pages into clean, readable text by using an open-source JavaScript library called Readability.js. When activated, this tool analyzes the underlying structure of a webpage, assigns scores to different sections based on text density and HTML tags, and isolates the highest-scoring section as the main article. Once the core text is identified, Firefox strips away the original website's styling, scripts, advertisements, and sidebars, injecting the remaining raw content into a minimalist template that users can customize for optimal reading.

1. Cloning the Webpage

When you load a webpage, Firefox does not alter the live page directly. Instead, it creates a hidden copy of the page's Document Object Model (DOM), which is the structural map of the webpage. Working on a clone ensures that the original page remains intact in case you exit Reader View, and it allows the browser to aggressively delete elements without breaking the live site.

2. Removing Obvious Clutter

Before looking for the article, the Readability algorithm performs a broad sweep to delete elements that never contain main article text. It immediately strips out:

  • All <script> and <style> tags, removing tracking codes, interactive ads, and the website's visual formatting.
  • Hidden elements that are not visible to the user.
  • Specific HTML tags associated with clutter, such as <nav>, <footer>, <aside>, and <form>.

3. Scoring the Content

To find the actual article among the remaining HTML, Firefox uses a heuristic scoring system. It scans the page for block-level elements—primarily <p> (paragraph), <div>, and <article> tags—and grades them based on their likelihood of being the main content.

Points are added for:

  • Semantic HTML tags or class names that contain words like "article", "body", "content", or "main".
  • High character counts within paragraphs.
  • The presence of multiple commas, which strongly indicates natural, written sentences rather than navigation menus or ad copy.

Points are deducted for:

  • Class names or IDs containing words like "comment", "sidebar", "footer", "promo", "ad", or "widget".
  • High "link density." If a block of text consists mostly of clickable links rather than plain text, the algorithm assumes it is a navigation menu, a list of related articles, or a sidebar, and penalizes it heavily.

4. Isolating the Main Article

As paragraphs are scored, their points are passed up to their parent containers (the <div> or <section> boxes that hold them). The parent container that accumulates the highest total score is declared the winner and is identified as the main body of the article. Everything outside of this winning container is completely discarded.

5. Secondary Cleanup

Even inside the winning article container, websites often embed inline advertisements, "Read More" links, and social media sharing buttons. Firefox runs a second pass inside the winning container to clean it up. It removes empty tags, strips out inline styling attributes, and deletes sub-containers that have a high link density or suspicious class names. It also extracts the article's title, author, and publication date from the page's metadata to display neatly at the top.

6. Applying the Reader View Template

Finally, Firefox takes the purified HTML—which now consists only of headings, paragraphs, blockquotes, and essential images—and places it into a brand-new, isolated document. Firefox applies its own internal Cascading Style Sheets (CSS) to this document. This default stylesheet provides a uniform font, wide margins, and a distraction-free background, while connecting the text to the Reader View sidebar controls so you can adjust text size, font type, and color themes.