manifest.json

{
  "name": "Pikachu Everywhere",
  "version": "0.1",
  "description": "Replace every image with Pikachu images.",
  "manifest_version": 2,
  "content_scripts": [{
      "matches": ["<all_urls>"],
      "all_frames": true,
      "js":      ["assets/js/contentScript.js"]
  }],
  "permissions": [
    "https://some-random-api.ml/*"
  ],
  "background": {
    "scripts": ["assets/js/background.js"],
    "persistent": false
  },
  "icons": {
    "16": "assets/images/icon16.png",
    "32": "assets/images/icon32.png",
    "48": "assets/images/icon48.png",
    "128": "assets/images/icon128.png"
  }
}