Examine source code of Back Button

{
  "description": "Back button",
  "manifest_version": 2,
  "name": "Back-button",
  "version": "1.0",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": {
      "16": "icons/left_16.png",
      "32": "icons/left_32.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{c75665c5-d3b9-426b-b3a7-a6671a9a9c5e}"
    }
  }
}