Examine source code of Image Forcer

{
  "manifest_version": 2,
  "name": "Image Forcer",
  "description": "Forces websites to return images of the correct type when requesting them. Prevents websites from returning HTML when requesting an image. Prevents website from returning WebP when requesting a PNG or JPEG/JPG.",
  "version": "1.0.0",
  "permissions": [
    "<all_urls>",
    "webRequest",
    "webRequestBlocking"
  ],
  "background": {
    "scripts": [
      "js/background.js"
    ]
  },
  "icons": {
    "32": "icons/32.png",
    "64": "icons/64.png",
    "128": "icons/128.png",
    "256": "icons/256.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "img-forcer@zipdox.net"
    }
  },
  "web_accessible_resources": [
    "*"
  ]
}