Examine source code of Add Bulk Mail - Expresso

{
  "manifest_version": 2,
  "name": "Add Bulk Mail - Expresso",
  "version": "1.2",
  "description": "Add multiple emails to a list at Expresso, removing duplicates.",
  "icons": {
    "48": "icons/navbar.png"
  },
  "permissions": [
    "storage",
    "notifications",
    "tabs"
  ],
  "browser_action": {
    "default_icon": {
      "32": "icons/mail_list.png"
    },
    "default_title": "Add Bulk Mail - Expresso",
    "default_popup": "popup/addbulkmail.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "popup/content_script.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{caf89178-f530-4c57-b6f9-2ddf3e54077e}"
    }
  }
}