Firefox で「混在コンテンツ」をブロックする仕様変更に対する対策。http ではなく、https に接続するように変更した。 cf. https://support.mozilla.org/ja/kb/how-does-content-isnt-secure-affect-my-safety

getFacebookPageFeed.js

(function(){
    var fbPage = function(){
      var that = {},	
    		_paths = location.pathname.split('/');
    	
    	var hasUserName = function(){ return _paths.length == 2; };
    
    	var feed = function(id){
    		var req = new XMLHttpRequest();
    		req.onload = function () {
    			location.href = "https://www.facebook.com/feeds/page.php?format=rss20&id=" + id;
    		};
    		req.open("GET", "https://graph.facebook.com/" + id);
    		req.send();		
    	};
    	
    	var getFeed = function(){
    		if (hasUserName()){
    			var req = new XMLHttpRequest();
    			req.onload = function () {
    			     feed(JSON.parse(this.responseText).id);
    			};
    			req.open("GET", "https://graph.facebook.com" + location.pathname);
    			req.send();	
    		} else {
                feed(_paths[3]);
    		}
    	};
    	that.getFeed = getFeed;
    
    	return that;
    };
    var fb = fbPage().getFeed();
})();