The Bliss Fire Press
So far I have tried out 5 programs that can display the contents of an .epub file on a PC, and are downloadable for free for use forever (with no trial periods before you pay money).
Nook Study (not to be confused with the other Nook)
EPUBReader for Mozilla Firefox (available as an add-on)
All of them have at least one thing wrong with them.
Nook for PC and Adobe don't recognize text-align:center in the book's CSS file, and they both display all elements over to the left instead of centered. The Mini-Manual in my book looks terrible. (They display correctly in the other 3 programs.) These two programs also have GUIs that are very difficult to figure out. (HINT: On the Adobe, there is a teeny weeny triangle next to the word LIBRARY in the upper left corner that you push to get the menu, which includes the help file.) Nook for PC has a worthless help file.
Adobe and Mozilla don't recognize fragmentary links, like File.htm#item. When you click on them, they just go to the beginning of the chapter file. My list of chant illustrations will take you to the beginnings of chapters instead of the ends where they are.
Mobipocket, Adobe, and Nook for PC have no back button to go to the previous page viewed, like when you've clicked on an endnote link and now you want to go back to the page you were at. If you make a jump, you have to click all the way back thru individual pages or go to the table of contents and start from the beginning of a chapter.
Of all of these, I think the best is Nook Study. It displays centerings and obeys links to internal id tags as well as an internet browser, and it has a "history" button which is as good as a back button. What would make it even better would be the ability to scroll vertically thru text line by line, instead of only jumping page by page, as you can do in Mobipocket, as well as having that program's thermometer bar at the bottom that tells you where you are in the whole text and lets you move thru it in an analog fashion. This special trength makes Mobipocket worth downloading in addition to Nook Study, for viewing books with long lists.
– Butterfly Bill