Examine source code of ProTick

{
  "manifest_version": 2,
  "name": "ProTick",
  "version": "1.0.2",
  "description": "A simple Firefox extension to download Canva graphics, images and shapes.",
  "icons": {
    "16": "icons/icon-16.png",
    "32": "icons/icon-32.png",
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  },
  "browser_action": {
    "default_popup": "popup/popup.html",
    "default_icon": "icons/icon-48.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "permissions": [
    "activeTab",
    "storage",
    "downloads"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://www.canva.com/design/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{3974eb11-b0b0-409b-83ea-59b1249946f5}"
    }
  }
}