Examine source code of Allure Image Sizer

{
  "browser_specific_settings": {
    "gecko": {
      "id": "allureImageSizer@allure.com"
    }
  },
  "browser_action": {
    "default_icon": {
      "128": "3huy4k0a8ez71.png"
    },
    "default_title": "Image Sizer",
    "default_popup": "popup.html"
  },
  "commands": {
    "toggle-feature": {
      "suggested_key": {
        "default": "Ctrl+Shift+Y",
        "linux": "Ctrl+Shift+U"
      },
      "description": "Send a 'toggle-feature' event"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "default_locale": "en",
  "description": "Resize and analyze images on Mozilla sites.",
  "icons": {
    "128": "3huy4k0a8ez71.png"
  },
  "manifest_version": 2,
  "name": "Allure Image Sizer",
  "permissions": [
    "webNavigation",
    "activeTab",
    "tabs"
  ],
  "version": "1.0",
  "web_accessible_resources": [
    "images/my-image.png",
    "popup.html",
    "popup.js",
    "popup.css"
  ]
}