Examine source code of Revealancer

{
  "manifest_version": 2,
  "name": "Revealancer",
  "version": "2.0",
  "description": "Reveal more info about projects in first page of freelancer.com.",
  "icons": {
    "48": "icons/rl-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.freelancer.com/*"
      ],
      "js": [
        "index.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "https://www.freelancer.com/*",
    "menus",
    "tabs",
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "strict_min_version": "57.0a1"
    }
  }
}