Firefox addon-sdk - document.activeElement not available on some pages

cs.js

(function() {

  self.port.on('init', init);

	function init(data) {
		var active = document.activeElement;
		if (!active) {
			console.log("Failed to get activeElement");
		}
		if (active != document.body) {
			console.log("got proper activeElement");
			console.log("type = " + document.activeElement.type);
			console.log("id = " + document.activeElement.id);
		}
		else {
			console.log("activeElement is not available");
		}

		console.log("data = " + JSON.stringify(data));
		if (data.id != "") {
			var elementById = document.getElementById(data.id);
			if (elementById == null) {
				console.log("failed to get document.getElementById()");
			}
			else {
				console.log('document.getElementById() is working');
			}
		}
	}

})();

main.js

(function() {
  var data = require("self").data,
	contextMenu = require("context-menu"),
    tabs = require('tabs');

	var workers = [];
	var pageMod = require("page-mod");
	var page = pageMod.PageMod({
		include: '*',
		contentScriptWhen: 'ready',
		contentScriptFile: data.url('cs.js'),
		onAttach: function(worker) {
			workers.push(worker);
			worker.on("detach", function() {
				var index = workers.indexOf(worker);
				if (index >= 0) workers.splice(index, 1);
			});
		}
	});

    function createContextMenu(kontext) {
        var english = contextMenu.Item({
            label: "English",
            data: 'en'
        }),
            french = contextMenu.Item({
                label: "French",
                data: 'fr'
            });
        var searchMenu = contextMenu.Menu({
            label: "My Addon",
            context: kontext,
            contentScriptWhen: 'ready',
            contentScript: "self.on('click', function(node, data) {self.postMessage({'data': data, 'id': node.id});});",
            items: [english, french],
            onMessage: function(data) {
                var worker = getActiveWorker();
                if (worker) {
                    worker.port.emit('init', data);
                }
            }
        });
        return searchMenu;
    };
    
    function getActiveWorker() {
        for (var i = 0; i < workers.length; i++) {
            if (workers[i].tab === tabs.activeTab) {
                return workers[i];
            };
        }
        return undefined;
    }

    var searchMenu = createContextMenu(contextMenu.SelectorContext("textarea, input"));
})();

thanks man , this helped me pretty much