Examine source code of Price Part Picker

{
  "manifest_version": 2,
  "name": "Price Part Picker",
  "description": "Display kakaku.com prices on PCPartPicker.com",
  "version": "1.0.1",
  "default_locale": "en",
  "browser_specific_settings": {
    "gecko": {
      "id": "ammar.githam@outlook.com"
    }
  },
  "background": {
    "scripts": [
      "js/backgroundPage.js"
    ]
  },
  "icons": {
    "16": "icon-16.png",
    "32": "icon-32.png",
    "48": "icon-48.png",
    "128": "icon-128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.pcpartpicker.com/*"
      ],
      "js": [
        "js/contentScript.js"
      ],
      "css": [
        "css/contentScript.css"
      ],
      "run_at": "document_start"
    }
  ],
  "permissions": [
    "storage",
    "*://*.kakaku.com/*"
  ]
}