Examine source code of WeTranslate

{
  "manifest_version": 2,
  "name": "W-Translate",
  "description": "Translate the selected text in current tab to any language by one click.",
  "version": "1.0.6",
  "icons": {
    "32": "icons/32.png",
    "64": "icons/64.png",
    "128": "icons/128.png",
    "256": "icons/256.png"
  },
  "browser_action": {
    "default_title": "W-Translate",
    "default_popup": "popup.html",
    "browser_style": true
  },
  "permissions": [
    "activeTab",
    "contextMenus"
  ],
  "background": {
    "scripts": [
      "scripts/background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_end",
      "css": [
        "css/content.css"
      ],
      "js": [
        "scripts/util.js",
        "scripts/content.js"
      ]
    }
  ],
  "web_accessible_resources": [
    "assets/*"
  ]
}