Examine source code of Tackle

{
  "manifest_version": 2,
  "name": "Tackle",
  "description": "Automatic Google Calendar time tracking and productivity insights",
  "version": "9.20.0",
  "icons": {
    "16": "/img/16.png",
    "48": "/img/16.png",
    "128": "/img/16.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "data_collection_permissions": {
        "required": [
          "websiteContent",
          "websiteActivity"
        ],
        "optional": [
          "technicalAndInteraction"
        ]
      },
      "id": "{afac0621-9db2-4cc0-8ca9-1bc22c980252}"
    }
  },
  "permissions": [
    "activeTab",
    "scripting",
    "storage",
    "https://app2.timetackle.com/*",
    "https://calendar.google.com/*",
    "https://core.timetackle.com/*"
  ],
  "web_accessible_resources": [
    "assets/*",
    "img/*",
    "assets/vendor/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Tackle",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "https://calendar.google.com/calendar/*"
      ],
      "all_frames": false,
      "run_at": "document_end",
      "css": [
        "content-scripts/content.css"
      ],
      "js": [
        "content-scripts/content.js"
      ]
    }
  ]
}