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)