Examine source code of TabFocus

{
  "manifest_version": 2,
  "name": "TabFocus",
  "version": "1.0",
  "description": "A simple tool to remind you to focus on one tab when switching frequently.",
  "icons": {
    "48": "icon.png"
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "permissions": [
    "tabs"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{e736e47e-72c4-43a3-b0a3-b9a79d54e7f0}"
    }
  }
}