Examine source code of ElementShot

{
  "manifest_version": 2,
  "name": "ElementShot",
  "description": "Pick any element and capture a screenshot with a highlighted border.",
  "version": "1.0.3",
  "icons": {
    "16": "icon/16.png",
    "32": "icon/32.png",
    "48": "icon/48.png",
    "128": "icon/128.png"
  },
  "permissions": [
    "activeTab",
    "downloads",
    "storage",
    "scripting",
    "<all_urls>"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "elementshot@alca.dev",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "options_ui": {
    "open_in_tab": true,
    "page": "options.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "ElementShot",
    "default_popup": "popup.html"
  },
  "content_scripts": []
}