Examine source code of Check All Checkboxes

{
  "manifest_version": 2,
  "name": "Check All Checkboxes",
  "version": "1.0",
  "description": "Check all checkboxes on the current page with one click",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_icon": "icon.png",
    "default_title": "Check All Checkboxes"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{2ff9f75e-6e2a-445d-a163-26f75c54a175}"
    }
  }
}