Bug reports or help requests are not valid 1 star reviews (as per this site's rules), because you aren't "reviewing" any functionality and it not working entirely is obviously neither normal nor the case for everybody. Your rating is permanent but your issue isn't inherent to the addon, so such ratings create a false score and aren't even a good way to ask for help or report a bug since we can't communicate and you neglected to mention a whole lot of basic information.

You probably have a conflicting addon installed or something. Try disabling any other image helpers, floating buttons, etc.

Mozilla really ought to make work of explaining that permission to users, because I'm seeing this confusion a lot. The problem with it is that an addon either has no permission at all to modify a webpage (which includes necessities like detecting an image and setting a background around it), or gets full access to everything in the page ("all your data"), there is no in-between. Hope that clears it up for you, and I'm glad you took the time to check out the code and correct your own remark. Very cooperative and sensible of you, thanks.