Examine source code of Image Alt Viewer

{
  "manifest_version": 2,
  "name": "Image Alt Viewer",
  "version": "1.0",
  "description": "Show ALT text on hover over images.",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{6a6ec89c-3036-440d-891e-47965a39d5b8}"
    }
  }
}