if(this.checked) {
    this.checked = false;
    clearInterval(this._checkLinksInterval);
    this._checkLinksInterval = 0;
}
else {
    this.checked = true;
    var opened = { __proto__: null };
    var initialTab = gBrowser.selectedTab;
    this._checkLinksInterval = setInterval(function() {
        if(gBrowser.selectedTab != initialTab) {
            self.doCommand(); // Turn off
            return;
        }
        var links = content.document.getElementsByTagName("a");
        for(var i = 0, len = links.length; i < len; ++i) {
            var h = links[i].href;
            if(h in opened)
                continue;
            opened[h] = true;
            setTimeout(function(h) { // Pseudo async
                var tab = gBrowser.addTab(h);
                setTimeout(function() {
                    gBrowser.removeTab(tab);
                }, 5000);
            }, 0, h);
        }
    }, 1000);
}
this.onDestroy = function() {
    this.checked && this.doCommand();
};