Examine source code of Reaction Overlay

{
  "manifest_version": 2,
  "name": "Reaction Overlay",
  "version": "2.4.7.1",
  "description": "Drops an animated reaction layer on the current tab and clears it automatically.",
  "browser_specific_settings": {
    "gecko": {
      "id": "{dd00037b-7168-47d3-a633-04659a84af47}",
      "strict_min_version": "101.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "icons": {
    "32": "graphics/icon32.png",
    "48": "graphics/icon48.png",
    "64": "graphics/icon64.png",
    "96": "graphics/icon96.png",
    "128": "graphics/icon128.png"
  },
  "permissions": [
    "activeTab",
    "storage"
  ],
  "background": {
    "scripts": [
      "scripts/background.js"
    ],
    "persistent": false
  },
  "browser_action": {
    "default_popup": "scripts/popup.html",
    "default_title": "Reaction Overlay",
    "default_icon": {
      "32": "graphics/icon32.png",
      "48": "graphics/icon48.png",
      "64": "graphics/icon64.png",
      "96": "graphics/icon96.png",
      "128": "graphics/icon128.png"
    }
  },
  "commands": {
    "react-now": {
      "suggested_key": {
        "default": "Alt+Shift+R"
      },
      "description": "Replay the last reaction"
    }
  },
  "web_accessible_resources": [
    "scripts/core.js",
    "scripts/content.js"
  ]
}