Examine source code of AllMediaBlocker

{
  "manifest_version": 2,
  "name": "AllMediaBlocker",
  "version": "0.1.0",
  "description": "Blocks all images and/or videos from loading.",
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "paygham@pm.me"
    }
  }
}