Examine source code of Trav.Tools

{
  "name": "Trav.Tools",
  "manifest_version": 2,
  "version": "0.1",
  "description": "Turns the page red when you click the icon",
  "permissions": [
    "activeTab",
    "tabs",
    "*://*.travian.com/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*.travian.com/*"
      ],
      "js": [
        "src/index.js"
      ],
      "all_frames": true,
      "run_at": "document_end"
    }
  ],
  "web_accessible_resources": [
    "src/inject.js"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{7f857f59-016d-4853-965c-25d92ec92d5a}"
    }
  }
}