Hi and welcome to MR, ams1 !
Katti's Cat has pointed you to the right place already. You definetely should give "FBReader" a try (have a look
over here and
here).
If you specifically prefer ebooks in epub-Format then you should also
have a look at EPUBReader, which is a firefox add-on for this format only. There is a
special subforum here.
Have fun and good
!
All the best from the Baltic Sea!