Examine source code of Calculation Pad

{
  "manifest_version": 2,
  "name": "Calculation Pad",
  "description": "Adds a jQuery based single page application with a text pad and spreadsheet for Thunderbird/SeaMonkey/Firefox",
  "homepage_url": "https://addons.thunderbird.net/en-US/thunderbird/addon/calculation-pad/",
  "version": "0.23",
  "content_security_policy": "default-src 'self'; script-src 'self' 'unsafe-eval';",
  "background": {
    "scripts": [
      "/background/background.js"
    ],
    "page": "/background/background.html"
  },
  "options_ui": {
    "open_in_tab": true,
    "page": "/options/page.html"
  },
  "permissions": [
    "tabs",
    "menus",
    "clipboardWrite"
  ],
  "browser_action": {
    "default_title": "CalculationPad",
    "default_label": "CalculationPad",
    "default_icon": "icons/CalcPad_128.png",
    "allowed_spaces": []
  },
  "applications": {
    "gecko": {
      "id": "CalculationPad@jaques",
      "strict_min_version": "91.0"
    }
  },
  "icons": {
    "32": "icons/CalcPad_32.png",
    "64": "icons/CalcPad_64.png",
    "128": "icons/CalcPad_128.png",
    "256": "icons/CalcPad_256.png"
  }
}