Examine source code of fllscrnbttn

{
  "manifest_version": 2,
  "name": "furusukurin",
  "version": "0.0.2.16",
  "description": "",
  "icons": {
    "48": "furusukurin48.png",
    "96": "furusukurin96.png"
  },
  "permissions": [
    "tabs"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "web_accessible_resources": [
    "font.woff2"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "buttons.js"
      ]
    }
  ]
}