good question, I didn't think about it until now
With the current version it wouldn't be possible because it's tied to Firefox. But I'm working on the new version which is now XUL based. XUL is the Mozilla language for GUIs.
In general it's possible to run XUL standalone but I have to check if everything would work without problems in the case of EPUBReader. Instead of Firefox you would have to install XULRunner, which is basically Firefox without the Firefox frontend.
So, in general this would be possible, but nevertheless you have to install software (XULRunner). Where would you see the advantage of this solution instead of using Firefox?