Examine source code of Language Switch

{
  "manifest_version": 2,
  "name": "Language Switch",
  "version": "2.12.0",
  "description": "__MSG_extensionDescription__",
  "browser_specific_settings": {
    "gecko": {
      "id": "{6e1ccc3a-6961-4b99-9455-e04cb868e7f9}",
      "strict_min_version": "59.0"
    }
  },
  "icons": {
    "24": "icons/languageswitch.svg",
    "32": "icons/languageswitch.svg",
    "50": "icons/languageswitch.svg"
  },
  "background": {
    "scripts": [
      "utils/iconupdater.js",
      "utils/storage.js",
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "contentscript.js"
      ],
      "all_frames": true,
      "run_at": "document_start"
    }
  ],
  "browser_action": {
    "browser_style": true,
    "default_icon": "icons/languageswitch.svg",
    "default_popup": "popup/choose_language.html",
    "theme_icons": [
      {
        "dark": "icons/languageswitch.svg",
        "light": "icons/languageswitch-light.svg",
        "size": 19
      }
    ]
  },
  "options_ui": {
    "page": "options.html",
    "browser_style": true,
    "open_in_tab": false
  },
  "permissions": [
    "storage",
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "default_locale": "en"
}