How to add welcome page

Sometimes it will be helpful to open welcome page immediately after first running of an extension. This is quite simple task. But it will allow to make your
extension more user-friendly.

const MY_EXT_PREF_BRANCH = "extensions.myext";
const Cc = Components.classes; 
const Ci = Components.interfaces; 

var myExt = {
    PREF_FIRSTRUN : MY_EXT_PREF_BRANCH + ".firstrun",

    PAGE_WELCOME : "http://www.myext.com/welcome",

    prefService : Cc["@mozilla.org/preferences-service;1"].
                  getService(Ci.nsIPrefBranch),


    load : function () {
        if (myExt.isFirstRun()) {
            setTimeout(myExt.openSuccessPage, 2000);
            myExt.prefService.setBoolPref(myExt.PREF_FIRSTRUN, false);
        }
    }

    isFirstRun : function() {
        return myExt.getBoolPref(myExt.PREF_FIRSTRUN, true);
    },

    openSuccessPage : function() {
        gBrowser.selectedTab = gBrowser.addTab(myExt.PAGE_WELCOME);
    },


    getBoolPref: function(prefname, prefdef) {
        try {
            return myExt.prefService.getBoolPref(prefname);
        } catch(e) {
            myExt.prefService.setBoolPref(prefname, prefdef);
            return myExt.prefService.getBoolPref(prefname);
        }
    }
}

window.addEventListener("load", myExt.load, false);