Examine source code of Rufus IXL

{
  "manifest_version": 2,
  "name": "Rufus IXL",
  "description": "He loves you",
  "applications": {
    "gecko": {
      "id": "aidand@firefoxport.org"
    }
  },
  "version": "1.1resigned1",
  "icons": {
    "16": "icon16.png",
    "32": "icon32.png",
    "48": "icon48.png",
    "64": "icon64.png",
    "128": "icon128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "http://www.ixl.com/*",
        "https://www.ixl.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ]
}