Examine source code of Headcrab

{
  "name": "Headcrab",
  "version": "1.5resigned1",
  "manifest_version": 2,
  "description": "Various helpers for software devs attached into Jira.",
  "applications": {
    "gecko": {
      "id": "headcrab@thorhanks.com"
    }
  },
  "permissions": [
    "*://*/*",
    "storage"
  ],
  "icons": {
    "48": "icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "css": [
        "content.css"
      ],
      "js": [
        "content.js"
      ]
    }
  ]
}