Have not tried it on Firefox in Android. Does this url work for you https://data.mo.ee ?

However, it should work with Chrome and we have an app as well: https://play.google.com/store/apps/details?id=ee.mo.rpg

I'll try to download Firefox and see if there are any errors to be fixed.

Edit: Downloaded Firefox 91.3.0 for Android and everything was working without any issues. Android version 10.