Examine source code of FocusMode

{
  "manifest_version": 2,
  "name": "Focus Mode",
  "version": "0.6resigned1",
  "description": "Focus on what is important on the web.",
  "icons": {
    "32": "icons/FM-32.png",
    "48": "icons/FM-48.png"
  },
  "permissions": [
    "<all_urls>",
    "activeTab",
    "tabs"
  ],
  "background": {
    "scripts": [
      "Clean_Page.js"
    ]
  },
  "browser_action": {
    "default_icon": "icons/FM-32.png",
    "default_title": "Focus Mode",
    "default_popup": "popup/popup.html"
  },
  "options_ui": {
    "page": "options.html",
    "browser_style": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{6ad1adc8-a205-41b3-9b9a-e4a40d4070ce}"
    }
  }
}