Originally Posted by ghostyjack
Seeing as when you store the epub in the FF profile, you seem to unzip it and store it uncompressed, could you analyse the content at the time of adding it to the epub library and then store the result somehow (as an index maybe)?
Yes, something like this was my initial idea. But I think, the idea of theducks sounds very interesting, because it's much easier to implement and will nevertheless probably deliver good (enough) results. Even if the method you described would be used, the progress calculation would still be a guess.