Examine source code of EyeSaver

{
  "manifest_version": 2,
  "name": "EyeSaver",
  "version": "5.0",
  "description": "Applies a semi-transparent orange layer over all tabs.",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "contentScript.js"
      ],
      "css": [
        "style.css"
      ]
    }
  ],
  "browser_action": {
    "default_icon": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{7544bc56-262c-4922-8831-8ffeeb50f902}"
    }
  }
}