Examine source code of WatchRPC

{
  "name": "WatchRPC",
  "version": "3.3.0",
  "manifest_version": 2,
  "description": "Lets you display what your watching on discord",
  "homepage_url": "https://waterwolf.tk/projects/watchrpc2",
  "icons": {
    "16": "static/icons/icon16.png",
    "32": "static/icons/icon32.png",
    "48": "static/icons/icon48.png",
    "64": "static/icons/icon64.png",
    "128": "static/icons/icon128.png",
    "256": "static/icons/icon256.png"
  },
  "background": {
    "scripts": [
      "dist/background.js"
    ]
  },
  "browser_action": {
    "default_icon": "static/icons/icon64.png",
    "default_title": "WatchRPC",
    "default_popup": "static/popup/index.html"
  },
  "permissions": [
    "tabs",
    "scripting",
    "webRequest",
    "http://localhost/*"
  ],
  "web_accessible_resources": [
    "dist/content-scripts/inject/WatchRPC_AppleMusic_Window.js"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://music.youtube.com/*",
        "*://open.spotify.com/*",
        "*://music.apple.com/*",
        "*://www.youtube.com/*"
      ],
      "run_at": "document_end",
      "js": [
        "dist/content-scripts/CommonUtils.js"
      ]
    },
    {
      "matches": [
        "*://music.youtube.com/*"
      ],
      "run_at": "document_end",
      "js": [
        "dist/content-scripts/WatchRPC_YTMusic.js"
      ]
    },
    {
      "matches": [
        "*://music.apple.com/*"
      ],
      "run_at": "document_end",
      "js": [
        "dist/content-scripts/WatchRPC_AppleMusic.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{e0393c57-3080-4310-96df-a01aa23c66c8}"
    }
  }
}