Examine source code of videoVolume

{
  "manifest_version": 2,
  "name": "videoVolume",
  "version": "1.2.3resigned1",
  "description": "Global Volume controller, controls all <video>s tags volume. Executed on every page.",
  "icons": {
    "48": "image.png"
  },
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "index.js"
      ]
    }
  ],
  "browser_action": {
    "default_icon": "image.png",
    "default_title": "videoVolume",
    "default_popup": "popupindex.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{7ad4abd3-2c1c-4b1c-9bc4-a244db26efa8}"
    }
  }
}