I don't think you need an add-on for this if you're already handy with CSS, just edit userContent.css and use a domain-specific query:<p><pre><code> @-moz-document domain(https://news.ycombinator.com) {...}</code></pre>
Just use Stylus.<p><a href="https://addons.mozilla.org/en-US/firefox/addon/styl-us/" rel="nofollow">https://addons.mozilla.org/en-US/firefox/addon/styl-us/</a>
Nice. One page I visit daily had a nice dark background, and a bright-white glaring input form next to the text-panel that can't be dismissed. Not any more. Thanks!
Negative recent reviews in Chrome Store are a problem. I don't want to experiment with an extension if others have done so already and are unhappy as a result.