My name is Alex and I am one of the Support Engineers at JW Player. I will be more than happy to assist you with your questions.
Our player does not officially support Firefox for Android. The main reason why our player does not work on it would be its lack of native support for MP4s or HLS streams. This explains why the players on the pages you linked to do not work, because they are serving HLS streams with MP4’s as a fallback, but Firefox for Android can’t play either.