EPUB (short for Electronic Publication) is an open ebook standard. Files have the extension .epub. EPUB is designed for reflowable content, meaning that the text display can be optimized for the particular display device. The format is meant to function as a single format that publishers and conversion houses can use in-house, as well as for distribution and sale. A lot of ebook related sites on the Internet offer their books in epub format. The format is especially popular on sites that provide access to free ebooks.

The Firefox web browser does not support the EPUB format by default, so you can only download the file to your local computer system if the website is not providing access to an online EPUB reader.

Now the Firefox add-on EPUBReader changes this by adding support for the EPUB format to Firefox. This means that you can read epub ebooks online in the web browser with this add-on. EPUBReader highjacks the download process of EPUB files on the system. It decompresses the files, processing them and making them available in a readable format in a new browser tab.

EPUB ebooks are divided into two columns on the page. The left column displays the index of the ebook, the right the contents and some controls at the bottom. Controls include text formatting options to increase or decrease the font size, navigate pages, access a library of locally stored ebooks or free online libraries or saving bookmarks to continue reading at the position at a later point in time.

The library navigator is very handy. It currently supports ebooks on archive.org and feedbooks. You can use the search function to find a specific ebook on either site, or browse the epub books by category or other factors such as popularity or upload date.

Each ebook is displayed with its title and author, and a short description. You can load a detailed description or the full ebook with a single click. EPUBReader offers settings to change the layout and table of contents. The program will use the book’s default formatting which you can change in the options. You are allowed to change fonts, backgrounds or the margin to customize the reading experience yourself.

EPUBReader is a handy Firefox extension, especially for users who regularly work with epub eBooks. Firefox users can download the add-on now from the official Firefox add-on repository.