Indeed uBlock Origin is the #1 reason I use Firefox on Android.

#2 is dark reader.

AdGuard works pretty well on iOS. I don’t think there is a way to do a ‘dark reader’ specifically though perhaps pages honour the OS’s ‘dark mode’ setting these days? I would guess support is spotty.

Sites that use the prefers-color-scheme media query honor the OS setting on iOS, but it obviously doesn't work on sites that haven't implemented it - Dark reader[0] takes a invert-colors approach and makes it a little easier on the eyes.

[0] https://addons.mozilla.org/en-US/firefox/addon/darkreader/

well adguard only have ip, domain names etc. I mean it has less context? Addon has more context about the webpage lets say it can remove ads belonging to DOM with id #ads-1 ?

Exactly, uBlock Origin it doesn't just block on domain. It can also remove certain CSS items. Even nag screens about cookies and adblockers :)

And in Europe, cookies / nag-popup-removers for all those GDPR compliance dialogs (though vanilla Firefox is becoming better in blocking trackers by default).