From my experience of using the extension, the add-on seems to be unsatisfactory at best, and unusable at worst. For instance, basically every site that I visited had the logo at the lop-left corner of the screen blend in with the background in terms of color. It will also sometimes just not work as expected, and by sometimes I mean almost all of the sites that I visit. Even the site on which I'm writing this review (addons(dot)mozilla(dot)org/) is in white mode while running the extension. You should really fix your utility before asking users to donate $10 (which happens immediately, mind you).