Examine source code of Broken Resources Finder

{
  "manifest_version": 2,
  "name": "Broken Resources Finder",
  "version": "1.2resigned1",
  "author": "Bastian Dupps",
  "description": "The scope of the Broken Resources Finder WebExtension is to detect unavailable web resources like images or stylesheets by scanning the currently visited website and its embedded stylesheets.",
  "homepage_url": "https://github.com/dupps/broken-resources-finder",
  "applications": {
    "gecko": {
      "id": "broken-resources-finder@dupps.it"
    }
  },
  "icons": {
    "48": "icons/broken_image_48.png",
    "96": "icons/broken_image_96.png"
  },
  "permissions": [
    "webRequest",
    "<all_urls>",
    "activeTab",
    "tabs"
  ],
  "browser_action": {
    "default_icon": "icons/broken_image_36.png",
    "default_title": "Broken Resources Finder",
    "default_popup": "popup/popup.html"
  },
  "background": {
    "scripts": [
      "background_scripts/resource_checker.js"
    ]
  }
}