The funny part: doesn't work on this page! :D
And, tho it's not too important to me- all those dark modes listed as options? They don't work at all.
I'd like Bernard, and all coders of extensions like his, to note that some crucial on-screen elements [like the "Rating" field with its 4 stars to click on for these reviews, are hidden when his (and other) dimmers are used.] Maybe it's not worth the work of fixing, but it is worth adding a warning, for confused and frustrated users.

Works really well across all websites, but its impossible to adjust the colors. I like the grey text on black background, but every link is really a distractingly bright blue. I went to options, and it listed a ton of "variations" but there was no apply button. I tried clicking a box, and restarting, but that didn't change it either. Why list all those color options if they don't change anything?

Unfortunately I can't submit this via your bug report system, since I keep getting an error message.

In Firefox 55.0.2 64-bit, when loading certain webpages (including http://mybrowseraddon.com/dark-mode.html) the browser displays an error message saying that the webpage is slowing down your browser. This happens all of the time on certain webpages (mybrowseraddon) and only some of the time on other webpages (duckduckgo.com). I am using Windows 10 Pro 64-bit.

I prefer Dark Background and Light Text by Mikhail Khvoinitsky: https://addons.mozilla.org/firefox/addon/dark-background-light-text/.
You should try it. There are some obvious differences. And then some:
- It works with internal Firefox pages.
- It works with Windows High Contrast theme.
- It doesn't break any add-on pop-up panel.
- On facebook, it preserves original site icons.

update: it is causing sites to crash or slow down (ebay) even if not turned on - so i have do deactivate it (tested with FF55 Win10-32bit)

could you please add a dark theme to the Firefox pages (blanc page, addon page, etc...) too?

some elements may disappear with dark mode on
works not on every page (addons.mozilla.org)??

overall it is a nice, small and easy to use addon. (i´m using the dark grey theme)