If your web browser is not able to download an ebook when you click on the download link, place your mouse pointer over the link, then right click and select "Save File As".
Currently Opera and Internet Explorer do not recognize the .epub file extension.
In Opera place your mouse pointer over the link, right click and select either "Save Linked Content As..." or "Save To Download Folder".
In Internet Explorer place your mouse pointer over the link, right click and select "Save Target As". When the download folder appears, Internet Explorer may try to change the file extension from .epub to .xml. In which case, change the file extension back to .epub either before or after downloading.