Workes very good, can recommend it to anyone.
However, I'm not using it anymore at the moment, because I somehow wasn't able to use any browser theme with it. Maybe I'm just too incompetent to find the right setting, but I if you want to use your usual Firefox theme I'd tell you not to use this.
But, as I said, I'm very impressed by the quality of the CSS filtering, and if you just care about that you should definitely give it a go.

As a person who prefers the dark themes rather than the blinding whiteness of most sites, I like this idea a lot. This extension works well for the purpose of displaying pages in dark mode. The only problem I've found is that it dramatically increases the time it takes to move between pages.

It works perfectly for nearly all sites. Would love the ability to easily specify custom colours for elements on a specific page though.

I'm browsing like ten hours a day, and this add-on takes care of my eyes. wouldn't want to be without it any more.

The extension itself is relatively good, but lacks the customizability of Midnight Lizard and like that extension, tends to reduce performance quite a bit.

A surprise when uninstalling the extension is that while most developers usually either show the sad emoticon while saying they're sorry and asking for feedback, Dark Reader merely wishes good luck. Hits worse than a sad face.

I genuinely support the extension, but Midnight Lizard offers a lot more customization, even considering the slow-down.

I loved Dark Reader, but it made some pages really slow to load :( It definitely helped with my eye discomfort on pages where Night Mode wasnt an option, but again.. slow to load pages, especially pages I used for work. Would use again if this could be fixed.

Great but seems like not working on stackoverflow recently

It works well, though my only criticism is that is slows down my browser.