Examine source code of MuteNewTabs

{
  "manifest_version": 2,
  "name": "MuteNewTabs",
  "version": "1.0",
  "description": "Mutes new tabs.",
  "icons": {
    "48": "icons/volume2-48.png"
  },
  "permissions": [
    "activeTab",
    "tabs"
  ],
  "browser_action": {
    "default_icon": "icons/volume1-32.png",
    "default_title": "MuteNewTabs"
  },
  "background": {
    "scripts": [
      "mutenewtabs.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{aeb2a620-1be5-40bf-9a50-23cc9e5cff9d}"
    }
  }
}