It will in the next version. Twitter changed it again.

Please send more details/examples to author@i-dont-care-about-cookies.eu, I'll be happy to check. Thanks!

There may be different reasons for that. Maybe the extension doesn't work on your side for some reason. Or you use private browsing but you didn't let this extension to work in it. Or you have some other extension interfering. Or you really visit websites the extension doesn't cover yet. There are tens of thousands of different cookie warnings, and many websites change theirs too frequently and make it more difficult to remove the pop-up easily. Feel free to report those websites properly (via the "report" link in extension's menu) or by writing directly to author@i-dont-care-about-cookies.eu. Thanks :)

It used to (and still could) work in regular Firefox for Android but Mozilla team decided to stop supporting all extensions (they now allow only a couple of handpicked extensions).

It works in "Firefox Nightly" though, but the installation procedure is a bit complicated. I tried it and it works well: https://blog.mozilla.org/addons/2020/09/29/expanded-extension-support-in-firefox-for-android-nightly/