Examine source code of FuriKani

{
  "name": "FuriKani",
  "description": "Removes furigana on websites based on your WaniKani level",
  "version": "0.7.2",
  "icons": {
    "16": "res/icon16.png",
    "48": "res/icon48.png",
    "128": "res/icon128.png"
  },
  "manifest_version": 2,
  "browser_action": {
    "default_popup": "src/popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "src/content.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "src/background.js"
    ]
  },
  "permissions": [
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{51094a40-dcd9-401e-9903-19846ae2a532}"
    }
  }
}