Examine source code of Mastery Lookup

{
  "manifest_version": 2,
  "name": "Mastery Lookup",
  "version": "1.6.0",
  "description": "Adds a link to see users Mastery Points from OP.gg",
  "icons": {
    "48": "icons/logo-icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.op.gg/*"
      ],
      "js": [
        "masterylookup.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{9760cabe-9145-4881-911a-b9a80b656875}"
    }
  }
}