Examine source code of button to quickly save

{
  "manifest_version": 2,
  "name": "Pinterest Save Button",
  "version": "1.0.0",
  "description": "Toolbar button to quickly save the current page or images to Pinterest (best-effort).",
  "permissions": [
    "activeTab",
    "tabs",
    "storage",
    "<all_urls>"
  ],
  "browser_action": {
    "default_title": "Pinterest Save",
    "default_popup": "popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content-script.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "content_security_policy": "script-src 'self' 'unsafe-eval'; object-src 'self'",
  "browser_specific_settings": {
    "gecko": {
      "id": "{da941b23-6387-433e-a9f9-0aa447532350}"
    }
  }
}