Examine source code of Open Dyslexic

{
  "name": "Open Dyslexic",
  "version": "1.1",
  "description": "Applies the OpenDyslexic font to all web pages.",
  "manifest_version": 2,
  "permissions": [
    "tabs",
    "storage",
    "http://*/*",
    "https://*/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_action": {
    "default_title": "Toggle OpenDyslexic font",
    "default_icon": "icon16.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "icons": {
    "16": "icon16.png",
    "32": "icon32.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "web_accessible_resources": [
    "icon16.png",
    "icon32.png",
    "icon48.png",
    "icon128.png",
    "content.js"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{f27ec0a3-6931-47bc-a3bf-abab7794674f}"
    }
  }
}