Question

I am attempting to use preferences in a Firefox extension. I am able to create and read these, but when I attempt to run a function when they are changed I encounter a problem. I am using the suggested framework from MDN (with modifications so it does what I want).
This is the exact code here:

observe: function(aSubject, aTopic, aData) {
if (aTopic != "nsPref:changed")
{
return;
}
switch (aData) {
    case "username":
        var prefManager = Components.classes["@mozilla.org/preferences-service;1"].getService(Components.interfaces.nsIPrefBranch);
        var username = prefManager.getCharPref("extensions.alexandriauplink.username");
        // extensions.myextension.pref1 was changed
        break;
    case "password":
        var prefManager = Components.classes["@mozilla.org/preferences-service;1"].getService(Components.interfaces.nsIPrefBranch);
        var password = prefManager.getCharPref("extensions.alexandriauplink.password");
        alert(password);
        break;
}
var password = prefManager.getCharPref("extensions.alexandriauplink.password");
var username = prefManager.getCharPref("extensions.alexandriauplink.username");
alert( "username:" + username +"|" + "password:" + password);
}

The problem is that when I change the preferences in the option dialogue, this function is triggered 3 times for each preference which is changed.
Thank you in advance if you are able to be of assistance.

Answer 1

As a commenter pointed out, this was caused by multiple windows of firefox being open – each one was firing the event.