Examine source code of Badge counter for Gmail

{
  "manifest_version": 2,
  "version": "0.1.1resigned1",
  "name": "Badge counter for Gmail",
  "description": "Get badge counter for a custom user search query. Click on the toolbar button opens the newest email.",
  "permissions": [
    "alarms",
    "storage",
    "contextMenus",
    "*://mail.google.com/mail/u/*"
  ],
  "icons": {
    "16": "data/icons/16.png",
    "18": "data/icons/18.png",
    "19": "data/icons/19.png",
    "32": "data/icons/32.png",
    "36": "data/icons/36.png",
    "38": "data/icons/38.png",
    "48": "data/icons/48.png",
    "64": "data/icons/64.png",
    "128": "data/icons/128.png",
    "256": "data/icons/256.png"
  },
  "homepage_url": "http://add0n.com/badge-counter.html",
  "browser_action": {
    "default_icon": {
      "16": "data/icons/16.png",
      "18": "data/icons/18.png",
      "19": "data/icons/19.png",
      "32": "data/icons/32.png",
      "36": "data/icons/36.png",
      "38": "data/icons/38.png",
      "48": "data/icons/48.png",
      "64": "data/icons/64.png"
    }
  },
  "background": {
    "persistent": false,
    "scripts": [
      "webext.js",
      "gmail.js",
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "all_frames": true,
      "run_at": "document_start",
      "matches": [
        "*://mail.google.com/*"
      ],
      "js": [
        "data/inject.js"
      ]
    }
  ],
  "options_ui": {
    "page": "data/options/index.html",
    "chrome_style": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{7772e4d6-bc35-4a37-8260-d3f466e0a757}"
    }
  }
}