Examine source code of Image Size Highlighter

{
  "manifest_version": 2,
  "name": "Image Size Highlighter",
  "version": "1.0",
  "description": "Show real image dimensions below each image when hovered.",
  "permissions": [
    "activeTab",
    "<all_urls>"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{06cbb96c-1de6-4f9f-93a4-6a07add22be5}"
    }
  }
}