hello, this addon hasn't been made available/ported for firefox on android (which can't run all the plugins available in the desktop version of the browser). you can find extensions compatible with firefox on android at https://addons.mozilla.org/android/

The anonymoX Extension listed at https://addons.mozilla.org/en-US/firefox/addon/anonymox/versions/ is for Firefox (on desktop). If the Extension author has made it for Android Firefox also then it would have listed "Firefox for Android" in Works with part.

The addons.mozilla.org defaults to the (desktop) Firefox by default as you have to look on top where it says "Other Applications" menu and select "Firefox for Android".