Examine source code of Mail from Duck

{
  "manifest_version": 2,
  "name": "Mail from Duck",
  "version": "0.2",
  "description": "Send messages from your private @duck.com address. Enter a recipient to generate an outgoing DuckDuckGo email address.",
  "icons": {
    "32": "icon32.png",
    "64": "icon64.png",
    "128": "icon128.png"
  },
  "permissions": [
    "tabs"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "@mailfromduck",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "browser_action": {
    "default_icon": {
      "32": "icon32.png",
      "64": "icon64.png",
      "128": "icon128.png"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "https://duckduckgo.com/email/settings/autofill"
      ],
      "js": [
        "content.js"
      ]
    }
  ]
}