Examine source code of FurAffinity Fav+ Button

{
  "manifest_version": 2,
  "name": "FurAffinity Fav+ Button",
  "version": "1.21",
  "description": "Adds a 'Fav+' button next to submissions on FurAffinity.",
  "permissions": [
    "storage",
    "https://www.furaffinity.net/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.furaffinity.net/msg/submissions/*"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "styles.css"
      ]
    }
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "icons": {
    "16": "icon16.png",
    "32": "icon32.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "web_accessible_resources": [
    "*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "furaffinity-fav-plus@example.com",
      "strict_min_version": "109.0"
    }
  }
}