Thank you for your addon which seems to be the lightest among the ones I've tried.
I don't understand why you have hard-coded all the theme settings but one. I'd like to have two or more custom themes to choose among, one dark and one light. I could hack the contents of .xpi file, replacing the settings of one or more of the 15 available themes, but so doing I will be forced to not update the addon...
The background image on bing.com doesn't seem to invert with either "invert image" or the entire extension. If you could add a quick fix as a CSS rule to invert the page, which seems to work on the Stylish extension, that'd be great. Thanks.