Examine source code of layout-trello-ff

{
  "manifest_version": 2,
  "name": "layout-trello-ff",
  "version": "1.2",
  "author": "Timmy Jose<zoltan.jose@gmail.com>",
  "description": "A Trello board view layout changer for Firefox - horizontal, vertical and mixed layouts",
  "icons": {
    "48": "icons/change_layout_48.png"
  },
  "permissions": [
    "tabs",
    "activeTab",
    "cookies",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background_scripts/background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.trello.com/b/*"
      ],
      "js": [
        "content_scripts/change_page_layout.js"
      ]
    }
  ],
  "browser_action": {
    "default_icon": {
      "48": "icons/change_layout_48.png"
    },
    "default_title": "layout-trello-ff",
    "default_popup": "popup/change_layout.html"
  },
  "browser-specific_settings": {
    "gecko": {
      "id": "foo@bar.com"
    }
  }
}