Examine source code of Spotify2Tabs

{
  "manifest_version": 2,
  "name": "Spotify2Tabs",
  "version": "1.2.0",
  "description": "Opens a UltimateGuitar tab based on the song currently playing.",
  "commands": {
    "activate": {
      "suggested_key": {
        "default": "Ctrl+Shift+Space",
        "mac": "Command+Shift+Space"
      },
      "description": "Opens a UltimateGuitar tab based on the song currently playing."
    }
  },
  "background": {
    "scripts": [
      "index.js"
    ]
  },
  "browser_action": {
    "default_icon": "assets/icons/spotify2tabs/256.png",
    "default_popup": "popup/settings.html"
  },
  "permissions": [
    "<all_urls>",
    "tabs",
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{29d4c8c8-fbec-4f3d-ac44-a97f95d8c42c}"
    }
  }
}