Examine source code of Chatshark

{
  "manifest_version": 2,
  "name": "Chatshark",
  "version": "2.0",
  "description": "Filters out spam messages on Fishtank Live chat.",
  "permissions": [
    "storage",
    "activeTab"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.fishtank.live/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start"
    }
  ],
  "applications": {
    "gecko": {
      "id": "chatshark@firefox.com"
    }
  },
  "browser_action": {
    "default_popup": "popup.html"
  }
}