Examine source code of Keeping Tabs

{
  "manifest_version": 2,
  "name": "Keeping Tabs",
  "version": "1.3",
  "description": "Smart tab numbering and keyboard navigation for unpinned tabs",
  "author": "Vamshi Kodipaka",
  "homepage_url": "https://github.com/vamshi-ka/keeping-tabs",
  "browser_specific_settings": {
    "gecko": {
      "id": "keeping-tabs@vamshi-ka.github.io",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "developer": {
    "name": "Vamshi Kodipaka",
    "url": "https://github.com/vamshi-ka"
  },
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png"
  },
  "permissions": [
    "tabs",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": "icons/icon-48.png",
    "default_title": "Keeping Tabs"
  },
  "commands": {
    "go-to-tab-1": {
      "suggested_key": {
        "default": "Ctrl+1",
        "mac": "Command+1"
      },
      "description": "Go to unpinned tab 1"
    },
    "go-to-tab-2": {
      "suggested_key": {
        "default": "Ctrl+2",
        "mac": "Command+2"
      },
      "description": "Go to unpinned tab 2"
    },
    "go-to-tab-3": {
      "suggested_key": {
        "default": "Ctrl+3",
        "mac": "Command+3"
      },
      "description": "Go to unpinned tab 3"
    },
    "go-to-tab-4": {
      "suggested_key": {
        "default": "Ctrl+4",
        "mac": "Command+4"
      },
      "description": "Go to unpinned tab 4"
    },
    "go-to-tab-5": {
      "suggested_key": {
        "default": "Ctrl+5",
        "mac": "Command+5"
      },
      "description": "Go to unpinned tab 5"
    },
    "go-to-tab-6": {
      "suggested_key": {
        "default": "Ctrl+6",
        "mac": "Command+6"
      },
      "description": "Go to unpinned tab 6"
    },
    "go-to-tab-7": {
      "suggested_key": {
        "default": "Ctrl+7",
        "mac": "Command+7"
      },
      "description": "Go to unpinned tab 7"
    },
    "go-to-tab-8": {
      "suggested_key": {
        "default": "Ctrl+8",
        "mac": "Command+8"
      },
      "description": "Go to unpinned tab 8"
    },
    "go-to-tab-9": {
      "suggested_key": {
        "default": "Ctrl+9",
        "mac": "Command+9"
      },
      "description": "Go to unpinned tab 9"
    },
    "go-to-pinned-tab-1": {
      "suggested_key": {
        "default": "Alt+1",
        "mac": "Alt+1"
      },
      "description": "Go to pinned tab 1"
    },
    "go-to-pinned-tab-2": {
      "suggested_key": {
        "default": "Alt+2",
        "mac": "Alt+2"
      },
      "description": "Go to pinned tab 2"
    },
    "go-to-pinned-tab-3": {
      "suggested_key": {
        "default": "Alt+3",
        "mac": "Alt+3"
      },
      "description": "Go to pinned tab 3"
    },
    "go-to-pinned-tab-4": {
      "suggested_key": {
        "default": "Alt+4",
        "mac": "Alt+4"
      },
      "description": "Go to pinned tab 4"
    },
    "go-to-pinned-tab-5": {
      "suggested_key": {
        "default": "Alt+5",
        "mac": "Alt+5"
      },
      "description": "Go to pinned tab 5"
    },
    "go-to-pinned-tab-6": {
      "suggested_key": {
        "default": "Alt+6",
        "mac": "Alt+6"
      },
      "description": "Go to pinned tab 6"
    },
    "go-to-pinned-tab-7": {
      "suggested_key": {
        "default": "Alt+7",
        "mac": "Alt+7"
      },
      "description": "Go to pinned tab 7"
    },
    "go-to-pinned-tab-8": {
      "suggested_key": {
        "default": "Alt+8",
        "mac": "Alt+8"
      },
      "description": "Go to pinned tab 8"
    },
    "go-to-pinned-tab-9": {
      "suggested_key": {
        "default": "Alt+9",
        "mac": "Alt+9"
      },
      "description": "Go to pinned tab 9"
    }
  }
}