Examine source code of Peek

{
  "name": "Peek",
  "description": "Peek at your favorite sites without breaking your flow.",
  "version": "4.0.1resigned1",
  "manifest_version": 2,
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "activeTab",
    "tabs",
    "<all_urls>",
    "bookmarks"
  ],
  "icons": {
    "48": "icons/peek.svg",
    "96": "icons/peek.svg"
  },
  "commands": {
    "toggle-peek-1": {
      "suggested_key": {
        "default": "Alt+Shift+1"
      },
      "description": "Open Peek"
    },
    "toggle-peek-2": {
      "suggested_key": {
        "default": "Alt+Shift+2"
      },
      "description": "Open Peek"
    },
    "toggle-peek-3": {
      "suggested_key": {
        "default": "Alt+Shift+3"
      },
      "description": "Open Peek"
    },
    "toggle-peek-4": {
      "suggested_key": {
        "default": "Alt+Shift+4"
      },
      "description": "Open Peek"
    },
    "toggle-peek-5": {
      "suggested_key": {
        "default": "Alt+Shift+5"
      },
      "description": "Open Peek"
    },
    "toggle-peek-6": {
      "suggested_key": {
        "default": "Alt+Shift+6"
      },
      "description": "Open Peek"
    },
    "toggle-peek-7": {
      "suggested_key": {
        "default": "Alt+Shift+7"
      },
      "description": "Open Peek"
    },
    "toggle-peek-8": {
      "suggested_key": {
        "default": "Alt+Shift+8"
      },
      "description": "Open Peek"
    },
    "toggle-peek-9": {
      "suggested_key": {
        "default": "Alt+Shift+9"
      },
      "description": "Open Peek"
    },
    "toggle-peek-0": {
      "suggested_key": {
        "default": "Alt+Shift+0"
      },
      "description": "Open Peek"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "jid1-xEAuRv8GzibUdw@jetpack"
    }
  }
}