CanvasBlocker is ready for Firefox on Android and was available before Fenix. But in Fenix they only allow a small set of WebExtensions (https://addons.mozilla.org/de/firefox/collections/4757633/7dfae8669acc4312a65e8ba5553036/). You can help to get CanvasBlocker part of this list by suggesting it to the recommended programm (https://github.com/kkapsner/CanvasBlocker/issues/553).