Turns My Computer into a Serviceable eBook Reader Without Extra Software Rated 4 out of 5 stars
With the fullscreen mode on, (while hiding the navigation toolbar), this addon makes reading actually quite nice.
It would be ideal if it had a search function, and if you could drag the progress bar to end up at a corresponding page, (or be able to select a page by number as opposed to a chapter, and if it gave page numbers). There's also a peculiar bug on my Firefox (19.0.2 for Mac) where the favicon will alternate with the "connecting" title and the respective epub document title.
At the end of the day, the drawbacks don't really hamper the full-screen reading experience, and this add-on is the best method I've found of having an ePub reader without requiring any additional separate applications.