Examine source code of Tabulous

{
  "manifest_version": 2,
  "name": "Tabulous",
  "version": "1.0",
  "description": "Tabulous lets you to open a new tab directly next to the one you are currently on by simply pressing Ctrl-Alt-T instead of the normal Ctrl-T.",
  "permissions": [
    "browserSettings",
    "tabs"
  ],
  "icons": {
    "48": "icons/logo48.png",
    "96": "icons/logo96.png"
  },
  "background": {
    "scripts": [
      "Tabulous.js"
    ]
  },
  "commands": {
    "open-tab-after-current": {
      "suggested_key": {
        "default": "Ctrl+Alt+T"
      },
      "description": "Open new tab next to current"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{518fe9d7-f05b-4cbb-96be-d00da61424c8}"
    }
  }
}