I'm thinking about demise of OpenBerg project. I's developer Yorick did a great job but he was not successful in building community of developers and as soon as he lost interest or was not able to pay his attention, the project died. It seems that for the long-term success of such complicated project as OpenBerg or EPUBReader a community of developers is necessary.
Currently there are even three projects which aim to build EPUB reader based on Mozilla platform : yours EPUBReader, Ordbrand's Lucifox and Lucidor
(thanks to Toller for the link!) and Infogrid's Azardi II. Focuses, visions and licences may vary, but there is much common in these projects - namely, building of the reader of EPUB publications on Mozilla platform, and this common aim can be ground for some collaboration. (Azardi I was open source and I think that Richard Pipe is openminded towards some opensource solution)
If Michael, Ordbrand and Richard Pipe could negotiate some kind of collaboration, it would mean an establishment of the small community of developers behind EPUB reader based on Mozilla!
I imagine that something like core reader functionality can be developed under some permissive opensource license (Mozilla Public, or MIT or BSD) from which then anyone could fork according his focus or vision. For example, currently EPUBReader has the best interface and usability, but Lucifox has full-text search and Azardi II promises to introduce feature of reading different pages in splitted window. Why should some reader software lack such functionality or why should any developer to spend his efforts at reimplementing some functionality which is already available in other reader?
Of course all this can sound nice in theory, but in reality it could be difficult or impossible to implement. But nobody can tell this without at first contacting other developers from similar projects.