Examine source code of GifForces

{
  "manifest_version": 2,
  "name": "GifForces",
  "version": "2.3",
  "description": "Now celebrate your ACs on codeforces with gifs. This extension sends notifications and displays gifs describing the result of your last submission",
  "icons": {
    "48": "icons/icon48.png",
    "64": "icons/icon64.png",
    "128": "icons/icon128.png"
  },
  "permissions": [
    "tabs",
    "https://codeforces.com/*",
    "https://m1.codeforces.com/*",
    "https://m2.codeforces.com/*",
    "https://m3.codeforces.com/*",
    "storage",
    "webRequest",
    "notifications"
  ],
  "browser_action": {
    "default_icon": "icons/icon48.png",
    "default_title": "GifForces"
  },
  "content_scripts": [
    {
      "matches": [
        "https://codeforces.com/*",
        "https://m1.codeforces.com/*",
        "https://m2.codeforces.com/*",
        "https://m3.codeforces.com/*"
      ],
      "js": [
        "content.js",
        "remove_element.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "web_accessible_resources": [
    "icons/*"
  ]
}