This add-on is really great for people like me who prefer to use dark mode/themes all over. My OS is also always on High Contrast with White text on Black backgrounds. Firefox's Colors doesn't help much because most websites are simply useless when viewed with overridden dark colors and High Contrast. So I thank the developer for really good and useful work!
However there seem to be issues with some sites (bugzilla.mozilla.org is completely dark with nothing visible; GitHub fares a little better but still unusable). Performance is also a big hindrance - page loads and scrolling are completely off with this extension enabled. I presume the Chrome version may not have these issues but I prefer Firefox and would like to see this extension working well with it.