Examine source code of Focus Current Tab

{
  "manifest_version": 2,
  "name": "Focus Current Tab",
  "version": "1.0",
  "description": "Dim all other tabs except the active one.",
  "permissions": [
    "tabs"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{9b5037c7-81cc-42f2-99a1-029037a30e0a}"
    }
  }
}