Examine source code of Redmine Timer

{
  "manifest_version": 2,
  "name": "Redmine Timer",
  "version": "1.0.12",
  "description": "The Redmine time tracking button for Firefox. Icons made by Freepik from www.flaticon.com.",
  "applications": {
    "gecko": {
      "id": "jid1-zT5AHUaIFOm4GQ@jetpack",
      "strict_min_version": "57.0"
    }
  },
  "developer": {
    "name": "Jeff Robertson",
    "url": "https://bitbucket.org/jprc8/redmine-timer-for-browsers/overview"
  },
  "icons": {
    "96": "icons/timer.svg"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": "icons/timer.svg",
    "default_title": "Click to start recording",
    "theme_icons": [
      {
        "dark": "icons/timer.svg",
        "light": "icons/timer_light.svg",
        "size": 96
      }
    ]
  },
  "options_ui": {
    "browser_style": true,
    "page": "options.html"
  },
  "commands": {
    "_execute_browser_action": {
      "suggested_key": {
        "default": "Alt+R"
      }
    }
  },
  "permissions": [
    "contextMenus",
    "activeTab",
    "storage",
    "notifications",
    "alarms",
    "webRequest"
  ],
  "optional_permissions": [
    "*://*/*"
  ]
}