Examine source code of Image Composition Overlay

{
  "manifest_version": 2,
  "name": "Image Composition Overlay",
  "version": "2.0",
  "description": "Adds photographic composition overlays to images in the context menu",
  "permissions": [
    "contextMenus",
    "activeTab"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "contentScript.js"
      ]
    }
  ],
  "web_accessible_resources": [
    "fibonacci-spiral-overlay.png"
  ],
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{3cd064c8-8aad-40c0-a321-5ccd1fd93612}"
    }
  }
}