Examine source code of Grammar Checker

{
  "manifest_version": 2,
  "name": "Grammar Checker",
  "version": "1.0",
  "description": "Check grammar for selected text.",
  "permissions": [
    "contextMenus",
    "activeTab",
    "storage",
    "https://api.languagetoolplus.com/"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{eba90766-9aa1-4278-842f-ef7da61f4d08}"
    }
  }
}