Examine source code of osu! difficulty filter

{
  "manifest_version": 3,
  "name": "osu! difficulty filter",
  "version": "0.1.4",
  "description": "filters osu! beatmaps by star difficulty",
  "permissions": [
    "activeTab",
    "scripting",
    "storage"
  ],
  "options_ui": {
    "page": "options.html"
  },
  "action": {
    "default_icon": {
      "16": "assets/ext-icon.png",
      "24": "assets/ext-icon.png",
      "32": "assets/ext-icon.png"
    },
    "default_title": "osu! difficulty filter",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{49bec086-6332-4908-9549-26a174ca1d2f}",
      "strict_min_version": "42.0"
    }
  }
}