Examine source code of Mute Tabs By Default

{
  "manifest_version": 2,
  "name": "Mute Tabs By Default",
  "version": "1.1",
  "description": "Automatically mutes all new tabs by default.",
  "applications": {
    "gecko": {
      "id": "{0c550efd-36bc-4145-a8c6-38c0a5d67fcc}",
      "strict_min_version": "68.0"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "tabs",
    "webNavigation"
  ],
  "icons": {
    "48": "icons/icon.png"
  }
}