Examine source code of Read Receipt Decliner

{
  "name": "Read Receipt Decliner",
  "version": "1.1",
  "manifest_version": 2,
  "description": "Automatically declines to send read receipts in Google Mail",
  "icons": {
    "16": "icon-16.png",
    "48": "icon-48.png",
    "128": "icon-128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://mail.google.com/*"
      ],
      "js": [
        "no-read-receipts.js"
      ],
      "all_frames": true
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{200b44ae-90ea-483f-9c0e-74711c9350ed}"
    }
  }
}