Examine source code of Progressive Immersion

{
  "manifest_version": 2,
  "name": "Progressive Immersion",
  "description": "A browser extension that progressively immerses you in a language.",
  "icons": {
    "48": "images/logo-48.png",
    "96": "images/logo-96.png"
  },
  "version": "0.9.1",
  "permissions": [
    "webRequest",
    "alarms",
    "storage",
    "downloads",
    "unlimitedStorage",
    "contextMenus",
    "https://translate.google.com/*"
  ],
  "browser_action": {
    "default_icon": "images/logo-32.png",
    "default_title": "Progressive Immersion",
    "default_popup": "popup/index.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "content_scripts/main.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background_scripts/main.js"
    ]
  },
  "options_ui": {
    "page": "options/index.html",
    "browser_style": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{a3c126ff-6110-44fe-9ed3-69fe13527289}"
    }
  }
}