Examine source code of Language Switcher

{
  "version": "0.1.1",
  "manifest_version": 2,
  "name": "Language Switcher",
  "short_name": "language-switcher",
  "background": {
    "page": "lib/chrome/background.html"
  },
  "homepage_url": "http://mybrowseraddon.com/language-switcher.html",
  "permissions": [
    "storage",
    "activeTab",
    "webRequest",
    "<all_urls>",
    "webRequestBlocking"
  ],
  "description": "Change the language header (accept-language) that websites see via toolbar popup",
  "browser_action": {
    "default_title": "Language Switcher",
    "default_popup": "data/popup/popup.html",
    "default_icon": {
      "16": "data/icons/16.png",
      "32": "data/icons/32.png",
      "48": "data/icons/48.png",
      "64": "data/icons/64.png"
    }
  },
  "content_scripts": [
    {
      "all_frames": true,
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_start",
      "js": [
        "data/content_script/inject.js"
      ]
    }
  ],
  "icons": {
    "16": "data/icons/16.png",
    "32": "data/icons/32.png",
    "48": "data/icons/48.png",
    "64": "data/icons/64.png",
    "128": "data/icons/128.png"
  }
}