Examine source code of kbs.im

{
  "name": "kbs.im",
  "description": "kbs.im but in an extension so you can have fake keyboard sounds.",
  "version": "1.6",
  "manifest_version": 2,
  "permissions": [
    "storage",
    "<all_urls>"
  ],
  "icons": {
    "16": "icons/16x16.png",
    "32": "icons/32x32.png",
    "48": "icons/48x48.png",
    "64": "icons/64x64.png",
    "128": "icons/128x128.png",
    "256": "icons/256x256.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "kbsim@ihaxu.com",
      "strict_min_version": "57.0"
    }
  },
  "browser_action": {
    "default_popup": "popup.html"
  },
  "background": {
    "page": "background.html"
  },
  "content_scripts": [
    {
      "all_frames": true,
      "match_about_blank": true,
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "contentscript.js"
      ],
      "run_at": "document_start",
      "exclude_matches": [
        "https://kbs.im/*"
      ]
    }
  ]
}