Examine source code of LeetCode Timer

{
  "manifest_version": 2,
  "name": "LeetCode Timer",
  "description": "LeetCode Timer is a Firefox extension for timing LeetCode problems",
  "homepage_url": "https://github.com/briankosw/leetcode-timer",
  "developer": {
    "name": "Brian Ko",
    "url": "https://github.com/briankosw"
  },
  "icons": {
    "64": "./dist/images/lct.svg"
  },
  "version": "0.2.0",
  "permissions": [
    "*://leetcode.com/problems/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://leetcode.com/problems/*"
      ],
      "js": [
        "./dist/content_script.js"
      ],
      "css": [
        "./dist/css/styles.css"
      ]
    }
  ],
  "web_accessible_resources": [
    "./dist/images/*.svg"
  ]
}