Examine source code of Twittelet

{
  "manifest_version": 2,
  "name": "Twittelet",
  "version": "0.1.0",
  "author": "avotoko",
  "description": "Makes bookmarklet executable on twitter.com and mobile.twitter.com",
  "icons": {
    "48": "icons/icon-48.png"
  },
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "*://twitter.com/*",
    "*://mobile.twitter.com/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Twittelet",
    "default_icon": {
      "48": "icons/icon-48.png"
    }
  },
  "applications": {
    "gecko": {
      "id": "twittelet@avotoko"
    }
  }
}