Beginning with version 89, released July 1, 2021, Firefox added important features to support PDF accessibility.

Recently, the browser’s built-in PDF viewer (PDF.js) has been updated to support filling PDF forms directly within Firefox to make life easier for the users. Previously, Firefox only supported displaying PDF forms, but it was not possible filling them within the browser: users had to print them, fill them by hand and then scan them back to digital form.
The on-going pandemic situation and the lockdown experienced in many parts of the world has made clear the importance of PDF forms when having to deal remotely with administrations, banks and many other realities, and has also highlighted the strategical importance of integrating accessibility into digital content.  When we talk about “accessible digital content” we refer to digital content that can be perceived, operated and understood by an audience as wide as possible, including people with visual disabilities who use Assistive Technology, such as screen reader, to access and read it, being this digital content a web page, an EPUB or a PDF file.

While investing time in the updating of PDF viewer to add form filling support, the PDF.js developers team decided to prioritize improving the accessibility of the PDF reader for users of Assistive Technology, which lead to adding support for tagged PDFs. “Tagged PDF”, as introduced in later version of the PDF specification, allows PDFs to create a logical structure that screen reader could use. This structure can be compared to the HTML hierarchy of DOM nodes, that is the hierarchical structure of web pages. Tagged PDFs contain extra tag information that a screen reader can recognize and deliver to users. When creating a tagged PDF, it is possible to tag headings, paragraphs, lists, tables, images and image descriptions (alt text), and table of contents. Having this structure makes navigating around the PDF much easier, allowing screen reader users to jump from heading to heading – which is a fundamental accessibility requirement for structured documents – or read paragraphs without unneeded pauses, granting a more natural reading experience and improving PDF usability ad accessibility.

Thank to this update, Firefox PDF viewer has now become a more accessible PDF viewer solution, with great benefits for everyone.

You can read the technical details of these implementations in the following source: Implementing form filling and accessibility in the Firefox PDF viewer