Examine source code of Want to Listen

{
  "manifest_version": 2,
  "name": "Want to Listen",
  "author": "The Digs.fm team",
  "version": "0.4",
  "description": "Quickly add releases from various music sites to your 'Want to Listen' list on Digs.fm",
  "homepage_url": "https://digs.fm",
  "icons": {
    "48": "icons/icon-48.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "activeTab",
    "https://digs.fm/queued/add-from-extension"
  ],
  "page_action": {
    "default_icon": "icons/icon-48.png",
    "default_title": "Want to Listen",
    "browser_style": true,
    "show_matches": [
      "https://www.discogs.com/master/*",
      "https://www.discogs.com/release/*",
      "https://open.spotify.com/album/*",
      "https://www.mixcloud.com/*/*",
      "https://*.bandcamp.com/album/*",
      "https://musicbrainz.org/release/*",
      "https://musicbrainz.org/release-group/*"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{ce6ec7bc-c5db-44eb-bc39-ec9bfc8e07cb}"
    }
  }
}