This problem can be be only solved by flash fallback for Firefox browsers. You can find following line in JS code
t.supportsMediaTag = (typeof v.canPlayType !== 'undefined' || t.isBustedAndroid ) ;
change to
t.supportsMediaTag = (typeof v.canPlayType !== 'undefined' || t.isBustedAndroid )&& ( !t.isFirefox) ;