Have you tried Lucidor? (lucidor.org). It's lightweight, runs freestanding or as a firefox plugin, and you can configure it to either copy the .epub to its own directory, or to leave the book where it was found. I can't speak for MAC, being windows atm, but it certainly does not update my files.
It has the occasional rough edge - its still in beta - but I like it for its clean simple interface.
Snowman
|