Examine source code of GitHub System Emoji

{
  "description": "Make GitHub use the system emoji font instead of serving ugly images.",
  "manifest_version": 2,
  "name": "GitHub System Emoji",
  "version": "1.0",
  "icons": {
    "48": "icon-48.png",
    "96": "icon-96.png"
  },
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "https://*.github.com/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "fix-github-emoji@wezm.net"
    }
  }
}