Examine source code of Buttercup

{
  "manifest_version": 2,
  "name": "Buttercup",
  "description": "Browser extension for Buttercup, the secure and easy-to-use password manager.",
  "version": "3.2.0",
  "icons": {
    "16": "manifest-res/buttercup-16.png",
    "48": "manifest-res/buttercup-48.png",
    "128": "manifest-res/buttercup-128.png",
    "256": "manifest-res/buttercup-256.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": "manifest-res/buttercup-256.png",
    "default_popup": "popup.html#/"
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "run_at": "document_end",
      "all_frames": true,
      "js": [
        "tab.js"
      ]
    }
  ],
  "permissions": [
    "clipboardWrite",
    "http://*/*",
    "https://*/*",
    "storage",
    "tabs",
    "unlimitedStorage"
  ],
  "web_accessible_resources": [
    "*.png",
    "*.jpg"
  ],
  "applications": {
    "gecko": {
      "id": "{10e7d273-2e63-47c9-82af-76c45dc1b624}"
    }
  }
}