Question

I listen for a onload event on a main window, then for a DOMContentLoaded event on each browser/tab (I need run the code inside a browser at the most) and flag with controlExecuted that the code was run on a browser.

window.addEventListener("load", function(){
    try{
        var controlExecuted = 0;
        var appcontent = document.getElementById("appcontent"); // browser
        if (appcontent && controlExecuted == 0)
            appcontent.addEventListener("DOMContentLoaded", function docLoader(e){
                appcontent.removeEventListener("DOMContentLoaded", docLoader, false);
                alert('run code')
                controlExecuted = 1;
            }, true);
    }catch(e){
        // log!
    }
}, false);

This not works. The code run several times depending of the number of browsers/tabs.

So how to run only one instance of code in a firefox addon?

Answer 1

Here the complete solution to run only one instance of code in a firefox addon using JavaScript code modules.

// modules/main.jsm
var EXPORTED_SYMBOLS = ["instancesControl"];

var instancesControl = {
    executed : 0,
    windowExecuting : 0,

    get : function(){
        return ++instancesControl.executed;
    },
    reset : function(){
        instancesControl.executed = 0;
    },
    getWindowExecuting : function(){
        return instancesControl.windowExecuting;
    },
    setWindowExecuting : function(id){
        instancesControl.windowExecuting = id;
    }   
};

The main calling code:

 // load instancesControl module
Components.utils.import("resource://my-own-alias/main.jsm");

// identify window that will execute the one-instance code
var util = window.QueryInterface(Components.interfaces.nsIInterfaceRequestor)
.getInterface(Components.interfaces.nsIDOMWindowUtils);
var windowID = util.outerWindowID;

// listen load window event 
window.addEventListener("load", function(){
    var appcontent = document.getElementById("appcontent");
    if (appcontent){
        // listen load content (on every tab)
        appcontent.addEventListener("DOMContentLoaded", function docLoader(e){
            appcontent.removeEventListener("DOMContentLoaded", docLoader, false);
            if (instancesControl.get() == 1){
                instancesControl.setWindowExecuting(windowID);

                // this code will run only once no matter
                // how many tabs or windows user opens.

            }
        }, true);
    }
}, false);

// re-init code if executing windows is closed
window.addEventListener("unload", function(){
    if (instancesControl.getWindowExecuting() == windowID){
        instancesControl.reset();
    }
}, false);

Sure that you can improve it. Comment using @nomikos if you do.
THX.