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"
    }
  }
}