Dark Reader just shows up in the addons section for me in fdroid Fennec, and Firefox mobile. I don't think you need to do anything special to get it to work.
Oh, thanks for letting me know. I have been using that little trick since they had first released that feature for unsupported addons and there were very few available then. That is good to know it is available in the supported list.
sprokolopolis|4 years ago