Go to the webpage where you want to download the ePub file and click on the download link. If you already downloaded the ePub file to your PC, just open it via the "File/File open" menu or drag the file on the Firefox window.
Now EPUBReader starts working: it downloads/opens the ePub file, uncompresses it and does some other processing. At the end it will present you the ready to read ePub file immediately!
EPUBReader created a page where all the ePub files, you downloaded/opened, are listed. You can open this page at four locations:
EPUBReader added a bookmark to this page called "ePub-Catalog" which you can find at the end of your bookmark list.
You find a new menuitem in your Firefox "Tools" menu, called "ePub-Catalog".
You can add a button to your Firefox toolbar. If you use Firefox 4.0 or later, the button has been added automatically.
When you are reading an ePub-file, you find a button in the bottom toolbar.