Excellent add-on! Congrats and thank you to the Dev.

I tested all possible add-ons available for dark themes.
I also tested lot of dark theme scripts (Stylus and similar).
Also tested lot of CSS' scripts at userContent.css.
And this add-on is the best one among other alternatives. It has the best gain/loss equation (lightweight = low system impact, average good web-page layouts etc). In brief, it will work fine for most of the websites.

Sadly, this add-on has two week points:
1) At least 50% of web-pages have a white-flash when loaded, reloaded etc
2) On "Style-sheet-processor" option, at least 30% of web-pages break (for 1 second) at the very beginning when they start to load.

I found these two problems above almost in every similar add-on.
Only CSS' scripts and Stylus' scripts etc eliminate white-flashes + web-page broken on loading. It will be a dream if the Dev (Mikhail Khvoinitsky) can solve these two issues.

Thank you in advance!

What this extension is doing is freaking amazing, think about all the different ways of styling websites that web developpers use and this extension gets them all into an easy on the eye at night colour scheme. Gotta say that this worked much better than I had anticipated (even on mobile phones!), but that doesn't mean it's perfect. Only issue I have is when swapping between sites while browsing the screen goes white for a very short time and back to black. You don't notice this on a white colour scheme, but it is quite overwhelming at night with this extension turned on. It's not too big of a deal and I doubt that can be fixed, but if it could that would make this extension impacable.

I love this add-on when they changed things up and I couldn't get it when they updated firefox I uninstalled the update and downloaded a old version of firefox so I could still use this add-on.

When all else fails DBLT saves the day!
So many Add-ons encounter problems, across all platforms and browsers. So whether I'm home or a public machine DBLT is my goto add-on.

Question: Can config per site be exported somehow and imported later or maybe config is saved as part of adon sync? It would help a lot.

Very useful, big compatibility with many sites i have tested on it !

Thank you very much! Firefox(desktop and mobile) should have a dark theme by default changeable in a simple way. It is very annoying that bright white when you are in a low light room and on mobile phones is stressful for the battery too. Cannot possibly understand why they don't make a light — dark theme by default.