Examine source code of QuietTune

{
  "manifest_version": 2,
  "name": "QuietTune",
  "version": "1.0",
  "description": "Per-domain/tab volume profiles. Set desired volume per domain and apply locally using WebAudio GainNode.",
  "icons": {},
  "permissions": [
    "storage",
    "activeTab",
    "tabs"
  ],
  "browser_action": {
    "default_title": "QuietTune",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{d1310f8f-f6e5-4142-b3f4-92c59156e588}"
    }
  }
}