Basic firefox addon not working

Question

I just tried to develope a simple hello world addon to firefox based on the ff45.0 update where you can upload an manifest.json to the about:debugging

My addon simply logs the URL of visited pages to the console. However at the moment i can't get anything more than display the icons.

manifest.joson
{

    "manifest_version": 2,
    "name": "Browser Antivirus",
    "version": "1.0",

    "description": "Keeps your browser safe",
    "icons": {
        "16": "icons/Shield_16.png",
        "32": "icons/Shield_32.png",
        "64": "icons/Shield_64.png"
    },

    "applications": {
        "gecko": {
            "id": "mail@mail.com",
            "strict_min_version": "45.0.0"
        }
    },

    "background":{
        "scripts": ["browser_antivirus.js"]
    }

}

browser_antivirus.js

browser.webRequest.onCompleted.addListner(function(details){
    console.log(details.url);
});
//https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/WebRequest/onCompleted
//https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Anatomy_of_a_WebExtension#Background_scripts