Examine source code of Google Mail Checker

{
  "manifest_version": 2,
  "name": "Google Mail Checker for Firefox",
  "version": "0.0.3",
  "description": "Opens your Gmail inbox when you click the button.",
  "homepage_url": "https://gitlab.com/michael-mml/ff-google-mail-checker",
  "icons": {
    "48": "icons/gmail.svg"
  },
  "permissions": [
    "tabs"
  ],
  "browser_action": {
    "default_icon": "icons/gmail.svg",
    "default_title": "Google Mail Checker"
  },
  "background": {
    "page": "background_page/google-mail-checker.html"
  },
  "web_accessible_resources": []
}