Examine source code of Read Mode Toggles

{
  "manifest_version": 2,
  "name": "Read Mode Toggle",
  "version": "1.0",
  "description": "Toggle Reader Mode on supported pages.",
  "permissions": [
    "tabs"
  ],
  "browser_action": {
    "default_title": "Toggle Reader Mode",
    "default_icon": {
      "48": "icon.png"
    },
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{7d6bafe9-4f41-4250-abb4-cebef5b4732f}"
    }
  }
}