Generally works well. Of course, there are cases when it hangs or makes a page unintelligible (for example, yandex.ru/search/?text=asdf shows a blank window). Fortunately there is an option to not apply to specific sites. Also the feature to resize/move the extension window is badly needed, to enjoy WYSIWYG effect). The manual would be handy.

It's incompatible with some streaming websites, causing the whole browser disconnected from internet.

super nice, would love a preview live for the changes to get the colours right

Prefiero desactivar la extensión al menos de momento porque veo que ralentiza muchas webs aunque se puede entender por el hecho de poner un modo oscuro forzado que suele funcionar bastante bien pero ultimamente con determinadas webs las ralentizaba demasiado.
Si trataba de desactivar la app para una determinada web; cosa que tenía una manera que además recordaba las webs en donde no querías que se activara, pues daba un fallo avisando como que había fallado. Desactivaba el modo oscuro pero desde que refrescaras la página o fueras a otra del mismo portal.... ok, otra vez el modo oscuro activado y ralentizado todo.
También he comprobado que al desactivar la extensión, en portales web como Aliexpress ya no se ponen por defecto en idioma ruso. Cosa que como español, me molestaba mucho porque me hacía muy dificil navegar por el portal de AliExpress sin que a dos click, se pusiera en idioma ruso.
Es una pena porque siempre he pensado que era buena extesión para usar un modo oscuro no nativo en las webs que visito, pero me parece que ultimamente no funciona nada bien y afecta a la velocidad del navegador Firefox.
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I prefer to deactivate the extension at least for the moment because I see that it slows down many websites although it can be understood by the fact of putting a forced dark mode that usually works quite well but lately with certain websites it slowed them down too much.
If you tried to deactivate the app for a certain website; something that had a way that also remembered the websites where you did not want it to be activated, as it gave a failure indicating that it had failed. It deactivated the dark mode but since you refreshed the page or went to another of the same portal ... ok, again the dark mode activated and slowed down everything.
I have also verified that when deactivating the extension, on web portals like Aliexpress they no longer default to the Russian language. Which, as a Spaniard, bothered me a lot because it made it very difficult for me to navigate the AliExpress portal without two clicks, it was put in Russian.
It's a shame because I've always thought it was a good extension to use a non-native dark mode on the websites I visit, but it seems to me that lately it doesn't work well at all and it affects the speed of the Firefox browser.

Fanstatic addon. 10x better than the Chrome equivalent