Nice Add-on (if you know hot to use it) Rated 5 out of 5 stars
I knew someone in the Mozilla community had this resolved. Thanks Mr. Li for your work.
I only suggest that you add a reference in the Add-on page on how to use it. Most people (including me) think that just double clicking the chm file will do the job (and we know that you have to go to the View --> Sidebar --> CHM Reader)