Examine source code of ShowProblemRating

{
  "manifest_version": 2,
  "name": "ShowProblemRating",
  "version": "3.1",
  "description": "Shows the rating of a codeforces problem separately in the sidebar",
  "icons": {
    "16": "icon16.png",
    "48": "icon48.png",
    "128": "icon128.jpg"
  },
  "browser_action": {
    "default_icon": "icon32.png",
    "default_title": "ShowProbRating"
  },
  "content_scripts": [
    {
      "matches": [
        "*://codeforces.com/*/problem*"
      ],
      "js": [
        "cfprobrating.js"
      ]
    }
  ]
}