Examine source code of TabBehavior

{
  "manifest_version": 2,
  "name": "TabBehavior",
  "version": "0.1.5resigned1",
  "description": "Changes tab opening and closing behavior.",
  "homepage_url": "https://github.com/mekras/TabBehavior",
  "applications": {
    "gecko": {
      "id": "tab-behavior@vsepofigu.ru",
      "strict_min_version": "57.0"
    }
  },
  "permissions": [
    "tabs"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "48": "assets/icons/tab-behavior-48.png"
  }
}