Examine source code of Reading Progress 1

{
  "manifest_version": 2,
  "name": "Reading Progress Bar",
  "version": "1.0",
  "description": "Shows a progress bar at the top of the page indicating how much you've scrolled. Toggle with the toolbar button.",
  "icons": {
    "48": "icon.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "browser_action": {
    "default_icon": "icon.png",
    "default_title": "Toggle reading progress"
  },
  "permissions": [
    "activeTab",
    "tabs"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "readingprogressbar-001@youraddons",
      "strict_min_version": "91.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": [],
        "description": "This extension does not collect, store, or transmit any user data."
      }
    }
  },
  "data_collection_permissions": {
    "collects_data": false,
    "description": "This extension does not collect, store, or transmit any user data."
  }
}