Examine source code of onlyactivetabs

{
  "name": "onlyactivetabs",
  "version": "1.6.1",
  "manifest_version": 2,
  "description": "Discard tabs other than active ones to free resources",
  "permissions": [
    "alarms",
    "storage",
    "tabs"
  ],
  "icons": {
    "48": "icons/48.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "browser_style": true,
    "default_icon": "icons/32.png",
    "default_title": "Discard tabs"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{1282af6e-66e3-4176-b58c-83c5e3299178}"
    }
  }
}