Examine source code of Gmail Ad killer

{
  "description": "Browser extension to delete the annoying and confusing gmail ads",
  "manifest_version": 2,
  "name": "Ad Free Gmail",
  "version": "0.1",
  "homepage_url": "https://github.com/MariosGeorgiou/AdFreeGmail",
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png"
  },
  "applications": {
    "gecko": {
      "id": "mariosge90@gmail.com_adfreegmail"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.mail.google.com/*"
      ],
      "js": [
        "killGmailAds.js"
      ]
    }
  ]
}