Examine source code of Slack When Ready

{
  "name": "Slack When Ready",
  "version": "0.0.6",
  "description": "Protect your focus... spend less time in Slack.",
  "applications": {
    "gecko": {
      "id": "firefox@slackwhenready.org"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "https://*.slack.com/*",
        "http://*.slack.com/*",
        "https://slackwhenready.org/*"
      ],
      "js": [
        "extension.js"
      ],
      "all_frames": true,
      "css": [
        "static/style/shared.css"
      ],
      "run_at": "document_start"
    }
  ],
  "icons": {
    "64": "static/icons/icon64.png",
    "128": "static/icons/icon128.png"
  },
  "browser_action": {
    "default_icon": {
      "64": "static/icons/icon64.png",
      "128": "static/icons/icon128.png"
    },
    "default_title": "Slack When Ready",
    "default_popup": "static/html/popup.html"
  },
  "manifest_version": 2,
  "permissions": [
    "storage",
    "activeTab",
    "cookies"
  ]
}