Examine source code of Sample Extension #12

{
  "manifest_version": 2,
  "name": "Sample Extension #12",
  "version": "1.0",
  "description": "This is sample extension #12.",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "sample-id-12@example.com"
    }
  }
}